Comparison of Process Options for Improving Backend-of-Line Reliability in 28 nm Node Technologies and Beyond

2011-05-20T09:00:00+09:00

Authors: Oliver Aubel, Christian Hennesthal, Meike Hauschildt, Jens Poppe, Jens Hahn, Juergen Boemmels, Markus Nopper, and Robert Seidel
This paper compares the most encouraging process options for improving electromigration performance in advanced technology nodes. Metal capping yields the best electromigration performance; however, this process is most challenging with respect to integration and may also suffer from significantly decreasing grain sizes in trench bottoms for future technologies. Alloying or silicidation techniques are less challenging to implement but can result in unacceptably high resistance increases. We analyze the respective results for each option and compare the performance on 45, 32, and 28 nm technology nodes. In addition, the impact of the various process options on stressmigration and time-dependent dielectric breakdown are discussed.

Role of Impurity Segregation into Cu/Cap Interface and Grain Boundary in Resistivity and Electromigration of Cu/Low-k Interconnects

Shinji Yokogawa and Yumi Kakuhara — 2011-05-20T09:00:00+09:00

Authors: Shinji Yokogawa and Yumi Kakuhara
The role of impurity segregation into the Cu/cap interface and grain boundary is discussed in terms of resistivity and electromigration (EM) lifetime. A Co-based metal capping, a CuAl seed, and new liners (Ti, Zr, and Hf) are compared as technologies for EM lifetime improvement. The roles of impurity in grain growth and electron scattering are investigated by residual resistivity measurement and physical analysis. The EM lifetime distribution and activation energy of lifetime are also investigated. The efficiency of EM improvements is discussed in terms of the trade-off characteristics of each technology during use. The EM improvement efficiency is categorized into three groups.

Improved Step Coverage of Cu Seed Layers by Magnetic-Field-Assisted Ionized Sputtering

2011-05-20T09:00:00+09:00

Authors: Yuta Sakamoto, Koukichi Kamada, Junichi Hamaguchi, Akifumi Sano, Yukinobu Numata, Shuji Kodaira, Satoru Toyoda, and Koukou Suu
The relationship between the ion flux of self-ionized sputtering and the static magnetic field supplied by DC coils was investigated by ion current measurements. The ion flux was clarified in order to increase the substrate ion current. The additional magnetic field perpendicular to the substrate increases the substrate ion current and decreases the side electron current. The suppression of Cu ion diffusion increases the substrate ion current of self-ionized sputtering and the current distribution depends on the magnetic field configuration. A stronger magnetic field in the region of the wafer edge is necessary to increase the substrate ion current. This condition results in an increase in bottom step coverage and any asymmetry at the wafer edge is also corrected.

New Copper Alloy, Cu(SnN_{x}), Films Suitable for More Thermally Stable, Electrically Reliable Interconnects and Lower-Leakage Current Capacitors

Chon-Hsin Lin — 2011-05-20T09:00:00+09:00

Authors: Chon-Hsin Lin
The Cu(SnN_{x}) alloy film formed in this study by doping a minute amount of Sn or SnN in a copper film via barrier-free Cu metallization method exhibits a good stability at high temperatures, an apparent improvement in adhesion and a greater electrical reliability, including low resistivity, lower leakage current in Cu(SnN_{x})-gate metal–oxide–semiconductor (MOS) capacitors, a longer time-dependent dielectric breakdown (TDDB) lifetime. The copper alloy films fabricated with this barrier-free Cu metallization method shall be suitable for application in future interconnects.

Prediction of Stress Induced Voiding Reliability in Cu Damascene Interconnect by Computer Aided Vacancy Migration Analysis

Haruhisa Shigeyama, Takenao Nemoto, A. Toshimitsu Yokobori, and — 2011-05-20T09:00:00+09:00

Authors: Haruhisa Shigeyama, Takenao Nemoto, A. Toshimitsu Yokobori, and
The method of computer aided vacancy migration analysis has been developed to predict the stress induced voiding (SiV) reliability. In this method, distribution of hydrostatic stress was calculated by the finite element analysis (FEA), and vacancy concentration distribution was calculated by the finite difference analysis (FDA). In this paper, SiV acceleration tests were conducted in various widths of Cu lines in organic ultralow-k dielectric (Cu/Ta/ULK/SiCN) or silicon oxide dielectric (Cu/Ta/SiO_{2}/SiCN) and these results were compared with the results of the vacancy migration analyses. The number of SiV failures increased in the line with width of 0.35 µm for Cu/Ta/SiO_{2}/SiCN interconnects and 0.20 µm for Cu/Ta/ULK/SiCN interconnects, respectively, under SiV acceleration tests. The results obtained by vacancy migration analysis show similar behavior as the results of SiV acceleration tests. These results reveal that the vacancy migration analysis is useful to predict reliability of interconnects.

Atomic Layer Deposition of Thin VN_{x} Film from Tetrakis(diethylamido)vanadium Precursor

2011-05-20T09:00:00+09:00

Authors: Mayumi B. Takeyama, Masaru Sato, Hiroshi Sudoh, Hideaki Machida, Shun Ito, Eiji Aoyagi, and Atsushi Noya
Thin vanadium nitride (VN_{x}) films were grown by atomic layer deposition using tetrakis(diethylamido)vanadium as a precursor and NH_{3} as a reactant. A growth rate of 0.1 nm/cycle without incubation time is obtained. Transmission electron microscopy reveals that a nanocrystalline texture in random orientation is characteristic of the VN_{x} film, which is favorable as an extremely thin barrier application. A low carbon impurity level (∼6 at.%) is achieved owing to acceleration of the transamination between the V(NR_{2})_{4} precursor and NH_{3}. The lowest resistivity of 120 µΩ cm is successfully achieved for the VN_{x} film prepared under optimized conditions.

Barrier Properties of Thin ZrN_{x} Films Prepared by Radical-Assisted Surface Reaction

2011-05-20T09:00:00+09:00

Authors: Masaru Sato, Mayumi B. Takeyama, Yuichirou Hayasaka, Eiji Aoyagi, and Atsushi Noya
We have prepared thin ZrN_{x} films at low temperatures without substrate heating. In the proposed process, radical species generated by the catalytic decomposition of NH_{3} molecules react on the sputtered Zr film to form ZrN_{x}. The barrier performance of the obtained 5-nm-thick ZrN_{x} film is as good as that prepared by reactive sputtering at 350 °C, indicating the usefulness of the proposed method in forming ZrN_{x} films at low temperatures. We have also demonstrated the general effectiveness of the method for ZrN_{x} preparation in addition to the previous result of TiN_{x}.

Ru/WN_{x} Bilayers as Diffusion Barriers for Cu Interconnects

Windu Sari, Tae-Kwang Eom, Sang-Hyeok Choi, and Soo-Hyun Kim — 2011-05-20T09:00:00+09:00

Authors: Windu Sari, Tae-Kwang Eom, Sang-Hyeok Choi, and Soo-Hyun Kim
Bilayers of Ru (7 nm)/WN_{x} (8 nm) prepared by sputtering were investigated as diffusion barriers between Cu and Si, and their performances were compared as a function of N_{2} flow rate during the deposition of WN_{x}. The Ru/WN_{x} bilayer diffusion barriers were stable upon annealing at up to at least 650 °C for 30 min while a Ru single layer (15 nm in thickness) failed after annealing at 450 °C owing to the formation of Cu silicide. Grazing-angle X-ray diffractometry results showed that the crystallinity of the WN_{x} film was degraded but that its nanocrystalline state preserved upon annealing at higher temperatures with increasing N_{2} flow rate during the deposition. These resulted in the better performance against Cu attack of bilayer diffusion barriers with the WN_{x} film prepared with a higher N_{2} flow rate.

Formation of Palladium Silicide Thin Layers on Si(110) Substrates

Risa Suryana, Osamu Nakatsuka, and Shigeaki Zaima — 2011-05-20T09:00:00+09:00

Authors: Risa Suryana, Osamu Nakatsuka, and Shigeaki Zaima
The formation of palladium silicide thin films from Pd/Si(110) and Pd/Si(001) systems with and without a Ti intermediate layer has been investigated. The existence of a Ti layer could improve the thermal stability of Pd_{2}Si thin layers in Pd/Ti/Si(001). In addition, an epitaxial or highly oriented Pd_{2}Si layer is formed in Pd/Ti/Si systems. However, the roughness of the Pd_{2}Si/Si interface is observed in Pd/Ti/Si(110) systems, while the flatnesses of the Pd_{2}Si/Si interface is observed in Pd/Ti/Si(001).

Mechanism Verification of Electrochemical Migration of Fine Cu Wiring

2011-05-20T09:00:00+09:00

Authors: Daiki Komatsu, Nobuya Takahashi, Toshiki Furutani, Ramesh Kumar Bhandari, Kenji Sato, Naoyuki Jinbo, and Takashi Kariya
The mechanisms of electrochemical migration and consequent insulation failure in fine-pitch Cu wiring (line/space = 3 µm/3 µm) are investigated. A model in which the migration takes place in the presence of water in a phenol-based resin–resin interface between biased Cu traces is proposed. Replacing the bottom resin layer by a SiN layer is found to be an effective method of considerably enhancing the leakage characteristics.

Isobutyl Silane Precursors for SiCH Low-k Cap Layer beyond the 22 nm Node: Analysis of Film Structure for Compatibility of Lower k-value and High Barrier Properties

2011-05-20T09:00:00+09:00

Authors: Hideharu Shimizu, Nobuo Tajima, Takeshi Kada, Shuji Nagano, and Yukihiro Shimogaki
To form SiCH films with a high carbon content using plasma-enhanced chemical vapor deposition (CVD), isobutyl trimethylsilane (iBTMS) and diisobutyl dimethylsilane (DiBDMS) were examined as precursors for a low-k cap layer and Cu diffusion barrier at the top of Cu lines. We elucidated the relationship between the structure of low-k SiCH films made from these newly developed precursors and their barrier properties against copper and oxygen diffusion. We also studied the relationship between the structure of SiCH and the deposition process under various RF plasma powers. A Monte Carlo simulation was employed to estimate the deposition profile in an overhang test structure. Fourier transform infrared spectroscopy (FT-IR) was used to analyze molecular structures. Our studies indicate that deposition conditions cannot dictate carbon content, but can control porosity/density. Precursor selection is thus an important factor in forming SiCH with a high carbon content that achieves both lower k and good barrier properties.

Electrical Characteristics of Novel Non-porous Low-k Dielectric Fluorocarbon on Cu Interconnects for 22 nm Generation and Beyond

2011-05-20T09:00:00+09:00

Authors: Xun Gu, Takenao Nemoto, Yugo Tomita, Akihide Shirotori, Kotaro Miyatani, Akane Saito, Yasuo Kobayashi, Akinobu Teramoto, Shin-Ichiro Kuroki, Toshihisa Nozawa, Takaaki Matsuoka, Shigetoshi Sugawa, and Tadahiro Ohmi
A novel non-porous low-k dielectric, fluorocarbon, deposited by new microwave excited plasma enhanced chemical vapor deposition was successfully integrated into Cu damascene interconnects for the first time. Electrical characteristics of fluorocarbon/Cu damascene lines are investigated. A compatible line to line leakage current to the one with porous low-k carbon doped silicon oxide and a low effective dielectric constant as a value of 2.5 are achieved. The novel non-porous ultralow-k dielectric, fluorocarbon, is considered as a promising candidate to extendible for 22 nm generation and beyond.

Evaluation of a New Advanced Low-k Material

2011-05-20T09:00:00+09:00

Authors: Evgeny A. Smirnov, Kris Vanstreels, Patrick Verdonck, Ivan Ciofi, Denis Shamiryan, Mikhail R. Baklanov, and Mark Phillips
New advanced low dielectric constant films (spin-on 2.0) with k = 2.0 were prepared by using a self-assembling technology and deposited by the spin-on method. The open porosity of the films was equal to 40% and they exhibit good mechanical properties (Young's modulus for the pristine sample, thermally cured, is 4.77 GPa and hardness is 0.54 GPa). The principal advantage of these films is the absence of sp^{2} carbon that is typically formed in porogen based plasma enhanced chemical vapor deposition (PECVD) films and causes high leakage current. The change of the film's properties after UV assisted thermal curing at T = 430 °C with lamps having different wavelengths (narrowband with λ= 172 nm and broadband lamp with λ> 200 nm) was studied. Electrical measurements show a small increase of the k-value, however FTIR spectroscopy shows no bulk and surface hydrophilization after the curing. Observed decreases in thickness and porosity indicate densification of the matrix.

Effects of Postetching Treatment on Molecular-Pore-Stacking/Cu Interconnects for 28 nm Node and Beyond

2011-05-20T09:00:00+09:00

Authors: Daisuke Oshida, Ippei Kume, Hirokazu Katsuyama, Toshiji Taiji, Takuya Maruyama, Makoto Ueki, Naoya Inoue, Manabu Iguchi, Kunihiro Fujii, Noriaki Oda, and Michio Sakurai
The effects of postetching treatment (PET) using carbon-containing gas on molecular-pore-stacking (MPS)/Cu interconnects were investigated. By using this technology, a 5% reduction in wiring capacitance was obtained as a result of the hardening of exposed MPS at the trench bottom. Via-chain yield improvement was also confirmed as a result of eliminating of etching residues in via-holes. These results indicate that high production yield and reliability can be obtained by PET for 28-nm-node complementary metal oxide semiconductor (CMOS) devices and beyond.

Influence of the UV Cure on Advanced Plasma Enhanced Chemical Vapour Deposition Low-k Materials

2011-05-20T09:00:00+09:00

Authors: Patrick Verdonck, Els Van Besien, Kris Vanstreels, Christos Trompoukis, Adam Urbanowicz, David De Roest, and Mikhail R. Baklanov
In a recent study, low-k thin films with low dielectric constant (≤2.1) and high Young's modulus (>5 GPa) were obtained by introducing a remote plasma step between the traditional plasma enhanced chemical vapour deposition and UV curing. This study shows that the UV curing step with a narrow band lamp with wavelength of 172 nm induced more network Si–O and Si–H bonds and more densification than the curing step with a broadband lamp with wavelengths higher than 200 nm. As a consequence, the dielectric constant of the narrow band cured film was slightly higher, but Young's modulus and hardness were much improved. Electrical characterization showed good breakdown voltages and a more than sufficient time dependent dielectric breakdown reliability. The broadband lamp was then used to form thicker films which retained very well the characteristics of the thin films.

Structure-Modification Model of Porogen-Based Porous SiOC Film with Ultraviolet Curing

2011-05-20T09:00:00+09:00

Authors: Yoshihiro Oka, Akira Uedono, Kinya Goto, Yukinori Hirose, Masazumi Matsuura, Masahiko Fujisawa, and Koyu Asai
The effect of ultraviolet (UV) curing on film properties of porogen based porous SiOC (P-SiOC) film was investigated. The P-SiOC films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using alkoxysilane and porogen (hydrocarbon). UV curing time was changed from 0 s to 1000 s. The variation of the k value and elastic modulus on the P-SiOC film with UV curing can be classified into three phases. From the behavior of pore density and free volume rate evaluated by using positron annihilation spectroscopy (PAS), the multiphase model for structural modification of P-SiOC film by UV curing was proposed. In addition, the optimum UV curing time for obtaining a superior P-SiOC film with lower k value and higher mechanical strength was determined.

Analysis of Sidewall Damage Layer in Low-k Film Using the Interline Dielectric Capacitance Measurements

2011-05-20T09:00:00+09:00

Authors: Takahisa Furuhashi, Nobuto Nakanishi, Masahiro Matsumoto, Shigenori Kido, Masakazu Okada, Yuichi Kawano, Yukinori Hirose, Masahiko Fujisawa, and Koyu Asai
We investigate a brief method extracting properties of damage layer in low-k film using the electrical measurement of Cu interconnects. In the electrical measurements, the capacitance measurement is useful for evaluating the damage layer in low-k film because the increase of k-value in low-k film affects directly the change of Cu interconnects capacitance. The interline capacitance including the damage layer can be described by a serial connected parallel-plate capacitor model. The analysis of electromagnetic field shows that the interline capacitance does not correspond to the capacitance of parallel-plate capacitor due to the fringe factors of interline capacitance. We can eliminate the fringe factors of interline capacitance by measuring the capacitances of different line heights and succeed in acquiring the relationship between the thickness and the dielectric constant of sidewall damage layer in low-k film.

Effectiveness of Dimethyl Carbonate and Dipivaloyl Methane Chemicals for Internal Repair of Plasma-Damaged Low-k Films

Shuji Nagano, Kaoru Sakoda, Satoshi Hasaka, and Kiyoteru Kobayashi — 2011-05-20T09:00:00+09:00

Authors: Shuji Nagano, Kaoru Sakoda, Satoshi Hasaka, and Kiyoteru Kobayashi
We propose the use of methylating chemicals to repair plasma-damaged sites in low-k films. Dimethyl carbonate (DMC) and dipivaloyl methane (DPM) were selected as the methylating chemicals to supply methyl (CH_{3}) groups into the bulk of damaged porous SiOCH films. The absorption of water into the damaged films was fully suppressed by the DMC repair treatment. The relative dielectric constant, which was increased from the value of 2.4 in the as-grown porous SiOCH film to 3.1 by plasma processes, recovered to 2.6 owing to the DMC treatment. In the case of the DPM repair treatment, the relative dielectric constant showed an almost full restoration from a value of 3.8 in the damaged film. To discuss the chemical reaction during the DMC repair treatments, SiO_{2} and the damaged porous SiOCH films subjected to the treatments were analyzed using time-of-flight secondary ion mass spectrometry and Fourier-transform infrared spectroscopy. The results can be explained using the model showing that the methyl and methoxy groups generated via the decomposition of DMC molecules react with silicon and oxygen sites in the films.

Analysis of A Novel Slurry Injection System in Chemical Mechanical Planarization

2011-05-20T09:00:00+09:00

Authors: Anand Meled, Yun Zhuang, Yasa Adi Sampurno, Siannie Theng, Yubo Jiao, Leonard Borucki, and Ara Philipossian
Slurry mean residence time (MRT), removal rate, and polishing defects were analyzed for a novel slurry injection system used in chemical mechanical planarization. The novel slurry injection system was placed adjacent to the wafer on the pad surface and slurry was injected towards the wafer through multiple holes in the trailing edge of the injector bottom. Results showed the novel slurry injection system provided more efficient slurry delivery to the pad–wafer interface and generated lower slurry MRT, higher removal rate, and lower polishing defects than the standard pad center area slurry application method currently used in the IC manufacturing industry.

Tribological, Thermal, and Kinetic Characterization of 300-mm Copper Chemical Mechanical Planarization Process

2011-05-20T09:00:00+09:00

Authors: Yubo Jiao, Yasa Adi Sampurno, Yun Zhuang, Xiaomin Wei, Anand Meled, and Ara Philipossian
In this study, the tribological, thermal, and kinetic attributes of 300-mm copper chemical mechanical planarization were characterized for two different pads. The coefficient of friction (COF) ranged from 0.39 to 0.59 for the D100 pad, indicating that boundary lubrication was the dominant tribological mechanism. In comparison, COF decreased sharply from 0.55 to 0.03 for the IC1000 pad, indicating that the tribological mechanism transitioned rapidly from boundary lubrication to partial lubrication. Consequently, the D100 pad exhibited higher pad temperatures and removal rates than the IC1000 pad. A two-step modified Langmuir–Hinshelwood model was used to simulate copper removal rates as well as chemical and mechanical rate constants. The simulated copper removal rates agreed very well with experimental data and the model successfully captured the non-Prestonian behavior. The simulated chemical rate to mechanical rate constant ratios indicated that the IC1000 pad generally produced a more mechanically controlled removal mechanism than the D100 pad.

Slurry Supplying Method for Large Quartz Glass Substrate Polishing

2011-05-20T09:00:00+09:00

Authors: Panart Khajornrungruang, Keiichi Kimura, Ryuji Yui, Nagisa Wada, and Keisuke Suzuki
Chemical mechanical polishing (CMP) has been used in polishing a photomask substrate in flat-panel display (FPD) manufacture. Moreover, the quadrilateral geometry of quartz glass used as the photomask substrate has been enlarged. However, the slurry cannot flow throughout the glass surface evenly owing to the enlarged substrate covering the center of the platen in the polishing process. In this work, we verified the beneficial of spreading slurry into a non-inflow region by the reinforced suction of the slurry supplied to the polishing pad through a hole at center of the platen. A fluorescent agent was used instead of the slurry for flow visualization.

Electrochemical Reactions During Ru Chemical Mechanical Planarization and Safety Considerations

2011-05-20T09:00:00+09:00

Authors: Shohei Shima, Yutaka Wada, Katsuhiko Tokushige, Akira Fukunaga, and Manabu Tsujimura
We analyzed electrochemical reactions during ruthenium (Ru) chemical mechanical planarization (CMP) using a potentiostat and a quartz crystal microbalance, and considered the potential safety issues. We evaluated the valence number derived from Faraday's law using the dissolution mass change of Ru and total coulomb consumption in the electrochemical reactions for Ru in acidic solution and slurry. The valence numbers of dissolved Ru ions were distributed in the range of 2 to 3.5. As toxic ruthenium tetroxide (RuO_{4}) has a valence number of 8, we were able to conclude that no toxic RuO_{4} was produced in the actual Ru CMP.

Diamond Conditioner Microwear Effect on Pad Surface Height Distribution in Tungsten Chemical Mechanical Polishing

Yohei Yamada, Masanori Kawakubo, and Kazunori Kadomura — 2011-05-20T09:00:00+09:00

Authors: Yohei Yamada, Masanori Kawakubo, and Kazunori Kadomura
In this study, the surface topographies of chemical mechanical polishing (CMP) pad samples for varying levels of diamond microwear of a conditioner have been measured using a confocal microscope and an X-ray computer tomography (CT) scanner. The experimental results showed that the increase in the pad debris on the pad surface reduced the pad height ratio of the asperity called the “top surface area (TSA) ratio”. In addition, the overall removal rate in tungsten CMP was more dependent on the TSA ratio after polishing than on that after conditioning because the pad surface condition became worse with deformed asperities and micropores due to the insufficient conditioning.

Study of Cu-Inhibitor State for Post-Chemical Mechanical Polishing Cleaning

2011-05-20T09:00:00+09:00

Authors: Ken Harada, Atsushi Ito, Yasuhiro Kawase, Toshiyuki Suzuki, Makoto Hara, Rina Sakae, Chiharu Kimura, and Hidemitsu Aoki
In order to reduce corrosion on the Cu surface in post-chemical mechanical polishing (CMP) cleaning, controlling the state of inhibitor layers is indispensable. In this study, to investigate the behavior of inhibitor layers in the cleaning process, Cu–benzotriazole (BTA) layers on CuO_{X} were analyzed by electrochemical measurements and surface analysis. Electrochemical measurements revealed that Cu(I)–BTA can prevent corrosion more efficiently than Cu(II)–BTA, and surface analysis revealed that the Cu(I)–BTA layer is thin, whereas the Cu(II)–BTA layer is bulky. The Cu(I)–BTA layer is effective in preventing corrosion of the Cu surface.

Tribological Effects of Brush Scrubbing in Post Chemical Mechanical Planarization Cleaning on Electrical Characteristics in Novel Non-porous Low-k Dielectric Fluorocarbon on Cu Interconnects

2011-05-20T09:00:00+09:00

Authors: Xun Gu, Takenao Nemoto, Yugo Tomita, Akinobu Teramoto, Shigetoshi Sugawa, and Tadahiro Ohmi
Damage reduction during planarization is strongly required to avoid scratch generation and the variation in the electrical properties of low-k dielectrics leading to yield loss in an integrated circuit after the implementation of an ultralow-k dielectric in Cu damascene interconnects. An optimum process condition to reduce damage on brush scrubbing in post-chemical–mechanical-planarization (post-CMP) cleaning was proposed for advanced nonporous organic ultralow-k dielectric fluorocarbon/Cu interconnects. Increasing brush rotation rate by decreasing down pressures results in the improvement in both electric properties and particle removal efficiency. The tribological effects of brush scrubbing in post-CMP cleaning on the electrical characteristics were explored. The brush scrubbing condition of a high brush rotation rate at low down pressures contributes to the suppression of damage generation.

Disappearance of Barrier Metal during Cu Chemical Mechanical Planarization Processing and Its Mechanism

2011-05-20T09:00:00+09:00

Authors: Hiroshi Asano, Akihito Yasui, Tatsuhiko Hirano, Kazusei Tamai, and Hitoshi Morinaga
The bald disappearance of barrier metal had been observed on the wafer after Cu chemical mechanical planarization (CMP) processing. It was speculated that this phenomenon occurs because the excessively oxidized Ta by electrochemical reaction with Cu ion was removed more easily than the normal Ta oxide around it. The inhibition of the electrochemical reaction is necessary to solve this phenomenon.

Development of Original End Point Detection System Utilizing Eddy Current Variation Due to Skin Effect in Chemical Mechanical Polishing

Takashi Fujita, Keita Kitade, and Toshiyuki Yokoyama — 2011-05-20T09:00:00+09:00

Authors: Takashi Fujita, Keita Kitade, and Toshiyuki Yokoyama
An original end point detection system was developed by making use of the skin effect in chemical mechanical polishing (CMP). The developed system utilizes a critical change in the eddy current due to the skin effect. The critical change is caused by the following two phases in the polishing process. The first phase is that the eddy current increases when the magnetic flux begins to penetrate the copper film as the film thickness reduces to less than `skin depth'. The next phase is that the eddy current fades out due to substantial elimination of the copper film by further polishing. Consequently, a prominent local maximum point of the eddy current emerges at the turning point between the two phases, which can be detected sensitively before the copper film is eliminated. It was demonstrated that the developed system gains a high sensitivity by making use of a critical change in the eddy current due to the skin effect without exposing the semiconductor device excessively to an intense magnetic flux.

Application of Novel Ultrasonic Cleaning Equipment That Uses the Waveguide Mode for the Single-Wafer Cleaning Process

2011-05-20T09:00:00+09:00

Authors: Kazunari Suzuki, Yasuhiro Imazeki, Ki Han, Shoichi Okano, Junichiro Soejima, and Yoshikazu Koike
We demonstrate single-wafer cleaning using waveguide-type ultrasonic equipment. The waveguide vibrates as a Lamb wave, and ultrasonic waves of 900 kHz, which is within the megasonic frequency range, radiate from the waveguide side. The waveguide creates a traveling wave field between the waveguide side and wafer surface owing to ultrasonic absorption into the water at the waveguide end. For a traveling wave field, the obtained particle removal efficiency (PRE) was as good as that obtained with conventional batch-type equipment, and cavitation bubble collapse, which induces pattern defects on semiconductor devices, was suppressed. Cavitation bubble collapse was observed using wafers coated with photoresist film, and images of sonoluminescence were captured with a charge coupled device (CCD) camera system.

Formation and Evaluation of Electroless-Plated Barrier Films for High-Aspect-Ratio Through-Si Vias

2011-05-20T09:00:00+09:00

Authors: Hiroshi Miyake, Fumihiro Inoue, Takumi Yokoyama, Tomohiro Shimizu, Shukichi Tanaka, Toshifumi Terui, and Shoso Shingubara
The formation of a diffusion barrier layer in a through-Si via (TSV) has been studied with a combination of nanoparticle catalyst and electroless plating (ELP). We used Au-nanoparticles (Au-NPs) or Pd-nanoparticles (Pd-NPs) as catalysts for ELP of Ni- and Co-alloy barrier layers. We studied deposition of Ni–B and Co–B films in high-aspect-ratio (AR) TSV. Then, we succeeded in controlling the deposition profile of Ni–B in a high-AR TSV by the addition of bis(3-sulfopropyl)-disulfide (SPS). SPS turned out to be an inhibitor of electroless plating of Ni–B. On the other hand, the Co–B film was deposited conformally without additive. The electrical resistivity of Cu after annealing Cu/barrier stacked structure suggests that Co–B has better thermal stability than Ni–B.

Diffusion Resistance of Low Temperature Chemical Vapor Deposition Dielectrics for Multiple Through Silicon Vias on Bumpless Wafer-on-Wafer Technology

2011-05-20T09:00:00+09:00

Authors: Hideki Kitada, Nobuhide Maeda, Koji Fujimoto, Yoriko Mizushima, Yoshihiro Nakata, Tomoji Nakamura, and Takayuki Ohba
Diffusion behavior of Cu in Cu through-silicon-vias (TSVs) fabricated using low-temperature plasma enhanced chemical vapor deposition (LT-PECVD) has been evaluated. Silicon oxynitride (SiON) barrier films were formed by LT-PECVD at 150 °C. Cu diffusion rate was found to increase with decreasing film density. The critical density and thickness for prevention of Cu diffusion into Si substrate have been estimated. In case of a film with density >60% of the bulk value and/or thickness >100 nm, no change of electrical resistance for stacked wafers containing TSVs was observed after 1000 cycles of thermal stress. According to above results, SiON film formed at 150 °C can be used for the TSV process without any degradation of electrical characteristics and reliability, enabling a reduction in total process temperature in the wafer-on-wafer technology.

Characterization of Local Strain around Through-Silicon Via Interconnects by Using X-ray Microdiffraction

2011-05-20T09:00:00+09:00

Authors: Osamu Nakatsuka, Hideki Kitada, Youngsuk Kim, Yoriko Mizushima, Tomoji Nakamura, Takayuki Ohba, and Shigeaki Zaima
We have demonstrated the characterization of the local strain structure in thinned Si layers for wafer-on-a-wafer (WOW) applications by using X-ray microdiffraction with a synchrotron radiation source. The microdiffraction reveals the fluctuation of strains in the thin Si layer around through-silicon via (TSV) interconnects with a sub-micrometer scale. We can separately estimated the in-plane and out-of-plane strain structures in the Si layer, and found that the anisotropic strain is induced in the Si layer between the TSV interconnects.

Development of High-Speed Copper Chemical Mechanical Polishing Slurry for Through Silicon Via Application Based on Friction Analysis Using Atomic Force Microscope

Jin Amanokura, Hiroshi Ono, and Kyoko Hombo — 2011-05-20T09:00:00+09:00

Authors: Jin Amanokura, Hiroshi Ono, and Kyoko Hombo
In order to obtain a high-speed copper chemical mechanical polishing (CMP) process for through silicon vias (TSV) application, we developed a new Cu CMP slurry through friction analysis of Cu reaction layer by an atomic force microscope (AFM) technique. A lateral modulation friction force microscope (LM-FFM) is able to measure the friction value properly giving a vibration to the layer. We evaluated the torsional displacement between the probe of the LM-FFM and the Cu reaction layer under a 5 nm vibration to cancel the shape effect of the Cu reaction layer. The developed Cu CMP slurry forms a frictionally easy-removable Cu reaction layer.

A Study of Digitally Controllable Radio Frequency Micro Electro Mechanical Systems Inductor

2011-05-20T09:00:00+09:00

Authors: Atsushi Shirane, Yutaka Mizuochi, Shuhei Amakawa, Noboru Ishihara, and Kazuya Masu
This work proposes a micro electro mechanical systems (MEMS)-based digitally controlled solenoid-inductor. The inductor is fabricated by using a MEMS process. 2-bit tuning characteristics are measured, and tuning linearity and Q-factor degradation due to switching loss are discussed. The linear inductance tuning from 1.7 to 2.2 nH was achieved at 2 GHz. A Q-factor of more than ten was observed in the frequency range of 1.2 to 7.4 GHz. The validity of the proposed inductor was confirmed by investigating the effect of switch resistance.

Improvement in Electrical Properties of Carbon Nanotube Via Interconnects

2011-05-20T09:00:00+09:00

Authors: Masayuki Katagiri, Yuichi Yamazaki, Makoto Wada, Masayuki Kitamura, Naoshi Sakuma, Mariko Suzuki, Shintaro Sato, Mizuhisa Nihei, Akihiro Kajita, Tadashi Sakai, and Yuji Awano
We report on the electrical properties of carbon nanotube (CNT) via interconnects with improvement in contact formations between the CNT via and metal electrodes. For the improvement of the bottom contact formation, a TiN/TaN multilayer on a Cu bottom wiring layer is applied to suppress formation of a highly resistive oxide layer on the TaN barrier layer. The top electrode formation with good coverage on CNTs reduces contact resistance. The current–voltage characteristics of ultrafine CNT via interconnects exhibit ohmic behavior. The resistance of the CNT via interconnect is inversely proportional to the via area, indicating that the CNT bundles are grown with uniform quality and density in various-diameter via holes.

Chemical Vapor Deposition of Nanocarbon on Electroless NiB Catalyst Using Ethanol Precursor

Toru Tanaka, Tomomi Sato, Yusuke Karasawa, and Kazuyoshi Ueno — 2011-05-20T09:00:00+09:00

Authors: Toru Tanaka, Tomomi Sato, Yusuke Karasawa, and Kazuyoshi Ueno
Nanocarbon materials have been expected as post-Cu interconnect materials for large-scale integrated circuits (LSIs). In this paper, we present a nanocarbon deposition process using electroless plated NiB as the catalyst, which features conformal deposition on patterned dielectric surfaces. It was found that carbon nanotubes (CNTs) and graphitic films were deposited on the electroless NiB by atmospheric pressure chemical vapor deposition (CVD) using ethanol as the precursor. The graphitic quality estimated from the Raman spectra of the nanocarbon on the NiB catalyst was equivalent to that on a sputter-deposited pure Ni catalyst. The nanocarbon shape was dependent on NiB thickness, and CNTs were grown on 10-nm-thick NiB and graphitic films were grown on 30 nm or thicker NiB. The deposition temperature can be lowered to 505 °C, although the graphitic quality was degraded. It is considered that the electroless catalysts can be effective for nanocarbon deposition on patterned dielectric surfaces.

Iridium Nanocrystal Thin-Film Transistor Nonvolatile Memory with Si_{3}N_{4}/SiO_{2} Stack of Asymmetric Tunnel Barrier

2011-05-20T09:00:00+09:00

Authors: Terry Tai-Jui Wang, Tien-Lin Lu, Chien-Hung Wu, Yu-Cheng Liu, Shih-Wei Hung, Ing-Jar Hsieh, and Cheng-Tzu Kuo
Iridium nanocrystals (Ir-NCs) lying on the Si_{3}N_{4}/SiO_{2} tunneling layer have been demonstrated and Ir-NC-assisted thin-film transistor nonvolatile memory devices were successfully developed. Results show that Ir-NCs with a number density of ∼6×10^{11} cm^{-2} and a particle diameter of 4 to 12 nm can successfully be fabricated as charge trapping centers. Owing to the asymmetric SiO_{2}/Si_{3}N_{4} tunneling layer that increases programming/erasing efficiency, a significant memory window of 5.5 V has potential to be applied to multibit memory devices. Furthermore, after 10^{4} s, the memory window is still about 4.0 V in logic states.

Phase Equilibria, Crystal Chemistry, and Physical Properties of Ag–Ba–Si Clathrates

Isolde Zeiringer, Ernst Bauer, Andriy Grytsiv, Peter Rogl, and Herta Effenberger — 2011-05-20T09:00:00+09:00

Authors: Isolde Zeiringer, Ernst Bauer, Andriy Grytsiv, Peter Rogl, and Herta Effenberger
In the Ag–Ba–Si system the clathrate type I solid solution, Ba_{8}Ag_{x}Si_{46-x}, ranges at 800 °C from Ba_{8}Ag_{4.3}Si_{41.7} [a = 1.04309(3) nm] to Ba_{8}Ag_{5.4}Si_{40.6} [a = 1.04613(5) nm]. For all clathrate compositions in this homogeneity region (4.3 ≤x ≤5.4) cubic primitive symmetry with space group Pm-3n was confirmed by X-ray powder diffraction assisted by X-ray single crystal analyses of Ba_{8}Ag_{4.9}Si_{41.1}. Site preference from X-ray refinement reveals that silver atoms preferably occupy the 6d site in random mixture with Si. Ba_{2}AgSi_{3} (Ba_{4}Li_{2}Si_{6} type, Fddd, a = 0.862, b = 1.493, and c = 1.965 nm), reported by Cardoso et al., was confirmed. Studies of transport properties for Ba_{8}Ag_{5}Si_{41} evidenced electrons as predominant charge carriers and the closeness of the system to a metal-to-insulator transition.

Characteristics of Chemical Bonds in CuInSe_{2} and Its Thin-Film Deposition Processes Used to Fabricate Solar Cells

Takahiro Wada and Tsuyoshi Maeda — 2011-05-20T09:00:00+09:00

Authors: Takahiro Wada and Tsuyoshi Maeda
CuInSe_{2} (CIS) is one of the I–III–VI_{2} compound semiconductors with a chalcopyrite-type crystal structure. The characteristics of chemical bonds in CIS differ from those of conventional III–V and II–VI compound semiconductors. The characteristics of chemical bonds in CIS are advantageous for the fabrication of high-quality CIS thin films used in solar cells. The reasons why the “three-stage process” and “selenization process” are used for the fabrication of high-efficiency solar cells are discussed on the basis of recent studies of chemical bonds in CIS.

Mechanism of “Controlled Atomic Defects”: Extension to the Ternary Systems

Elena Rogacheva — 2011-05-20T09:00:00+09:00

Authors: Elena Rogacheva
The method of “controlled atomic defects” realized by changing the alloy composition along definite sections in the Gibbs triangle is applied to ternary phases of two types: ternary compounds and solid solutions based on binary compounds. The overview of extensive experimental material, which we obtained when studying I–III–VI_{2} ternary phases and IV–X–VI phases based on IV–VI binary compounds is given. The controlled introduction of non-stoichiometric and impurity defects of different types into I–III–VI_{2} and IV–VI compounds was realized using the “controlled atomic defects” method. It was shown that there is a distinct correlation between the composition, type and concentration of impurity and non-stoichiometric defects, on the one side, and the crystal structure and physical properties, on the other side. The results obtained prove the fruitfulness of using the “controlled atomic defects” method for the development of physical foundations of controlling properties of complex semiconductor phases.

Room-Temperature Ferromagnetism in (Zn,Mn,Sn)As_{2} Thin Films Applicable to InP-Based Spintronic Devices

Naotaka Uchitomi, Hiroto Oomae, Joel T. Asubar, Hironori Endo, and Yoshio Jinbo — 2011-05-20T09:00:00+09:00

Authors: Naotaka Uchitomi, Hiroto Oomae, Joel T. Asubar, Hironori Endo, and Yoshio Jinbo
We investigated the growth and magnetic properties of ternary ZnSnAs_{2} thin films doped with a various degrees of Mn content. It was confirmed that Mn-doped ZnSnAs_{2} thin films are pseudomorphically grown on nearly lattice-matched InP(001) substrates. Magnetization measurements on Mn-doped ZnSnAs_{2} thin films revealed a ferromagnetic transition temperature of around 330 K, and clearly showed hysteresis loops even at room temperature. No evidence of magnetic secondary-phase MnAs formation in the host ZnSnAs_{2} thin films was observed within the limit of our measurement system. We also prepared a trilayer structure consisting of Mn-doped ZnSnAs_{2} layers and an undoped ZnSnAs_{2} intermediary layer as a preliminary structure for a tunneling magnetic junction. This structure was confirmed to demonstrate ferromagnetism at room temperature. The present results suggest that diluted ferromagnetic (Zn,Mn,Sn)As_{2} thin films are one of the most promising building blocks for InP-based spintronic devices.

Epitaxial Growth of Chalcopyrite-Type CuInS_{2} Films on GaAs(001) Substrates by Evaporation Method with Elemental Sources

Nozomu Tsuboi, Takashi Tamogami, and Satoshi Kobayashi — 2011-05-20T09:00:00+09:00

Authors: Nozomu Tsuboi, Takashi Tamogami, and Satoshi Kobayashi
The structural properties of epitaxial CuInS_{2} thin films with various [Cu]/[In] ratios grown on GaAs(001) by the co-evaporation method with three element-sources are reported in comparison to those of the films on GaP(001). For the In-rich and almost stoichiometric films, the CuIn_{5}S_{8} phase and metastable CuAu-type ordering of the CuInS_{2} phase were exhibited. The Cu-rich films had sphalerite-type ordering of the CuInS_{2} phase. The slightly Cu-rich films had the c-axis oriented chalcopyrite-type CuInS_{2} structure with traces of the CuAu-type ordering and twins. Taking account of the fact that the slightly Cu-rich films on GaP had only the c-axis oriented chalcopyrite-type structure, the traces are considered to be due to the larger lattice mismatch for GaAs than for GaP. Broad photoluminescence emission bands in the band-edge region of the films, which could be related to shallow levels, were observed at low temperature.

Peculiarities of Linear Thermal Expansion of CuInS_{2} Single Crystals

Akira Nagaoka, Kenji Yoshino, Tomoyasu Taniyama, and Hideto Miyake — 2011-05-20T09:00:00+09:00

Authors: Akira Nagaoka, Kenji Yoshino, Tomoyasu Taniyama, and Hideto Miyake
CuInS_{2} single crystals were grown by a traveling heater method, which is one of the solution growth techniques. The temperature dependence of the X-ray diffraction of CuInS_{2} was determined between 10 and 300 K. The lattice constant of the a-axis decreased and that of the c-axis increased with increasing temperature. The linear thermal expansion of the c-axis calculated from the lattice constants decreased from 10 to 100 K.

Morphological and Structural Changes in Cu(In,Ga)Se_{2} Thin Films by Selenization Using Diethylselenide

Tomoaki Sato, Yoshifumi Kawasaki, Mutsumi Sugiyama, and Shigefusa F. Chichibu — 2011-05-20T09:00:00+09:00

Authors: Tomoaki Sato, Yoshifumi Kawasaki, Mutsumi Sugiyama, and Shigefusa F. Chichibu
The morphological and structural changes in Cu(In,Ga)Se_{2} (CIGS) thin films during selenization using diethylselenide (DESe) are investigated. The surface morphology and extra phase existence of CIGS thin films strongly depend on the heating profile temperature and time of each step during selenization. Conventional high-temperature (515 °C) selenized CIGS thin films formed grains of approximately 2–3 µm, although the Cu–In–Ga metallic precursor was very smooth. On the other hand, the precursor selenized at a low temperature (about 400 °C) exhibited a homogeneous surface morphology because the precursor was formed from Cu–Se and (In,Ga)–Se alloys to diffuse selenide into a Cu–In–Ga metallic precursor. The high-temperature selenized CIGS thin films after low-temperature selenization had a homogeneous surface morphology with appropriate-sized grains. These results indicate that the heating profile “during” selenization was very important in forming Cu–Se and (In,Ga)–Se alloys from a Cu–In–Ga metallic precursor.

Effect of H_{2}S Annealing on Ag-Rich Ag–In–S Thin Films Prepared by Vacuum Evaporation

2011-05-20T09:00:00+09:00

Authors: Yoji Akaki, Kyohei Yamashita, Tsuyoshi Yoshitake, Shigeuki Nakamura, Takahiro Tokuda, and Kenji Yoshino
We investigated the effect of H_{2}S annealing on Ag–In–S thin films prepared by vacuum evaporation. In thin films annealed above 350 °C, diffraction peaks except chalcopyrite AgInS_{2} phase were not observed for a starting material ratio of 1.0 but observed for that of 1.2. Thin films annealed at 400 °C with a starting material ratio of 1.5 contained several phases. We found that the Ag/In ratios of the films could be controlled by changing the starting material ratio. Grains of films with composition ratios of 1.0 and 1.2 were nonuniform, whereas those with a composition ratio of 1.5 were uniform.

Growth of Cu(In,Al)(S,Se)_{2} Thin Films by Selenization and Sulfurization for a Wide Bandgap Absorber

2011-05-20T09:00:00+09:00

Authors: Chika Fujiwara, Tomoaki Sato, Yoshifumi Kawasaki, Mutsumi Sugiyama, and Shigefusa F. Chichibu
The sequentially chalcogenization growth of Cu(In_{1-x}Al_{x})(S_{y}Se_{1-y})_{2} (CIASSe) films while controlling the S/(S+Se) ratio was demonstrated using Cu–In–Al precursor [Al/(Al+In)≤0.05]. These processes of sulfurization following selenization and selenization following sulfurization might be diffusion- and reaction-limited, respectively. Therefore, selenization following the sulfurization of Cu(In,Al)S_{2} may be suitable for controlling the S/(S+Se) ratio by process temperature and time. These results represent the first step toward realizing a solar cell using a CIASSe film grown by sulfurization and selenization using conventional and large-scale equipment.

Annealing Temperature Dependence of Properties of Cu_{2}ZnSnS_{4} Thin Films Prepared by Sol–Gel Sulfurization Method

Kazuya Maeda, Kunihiko Tanaka, Yuya Nakano, and Hisao Uchiki — 2011-05-20T09:00:00+09:00

Authors: Kazuya Maeda, Kunihiko Tanaka, Yuya Nakano, and Hisao Uchiki
Cu_{2}ZnSnS_{4} (CZTS) thin films were fabricated by a sol–gel sulfurization method with a rapid thermal process. The films preheated at 250 °C for 1 h and sulfurized from 350 to 600 °C for 1 h were investigated. The chemical composition of sulfur was 40% for the preheated film and 50% for the films sulfurized at temperatures higher than 400 °C. The grain size of the films markedly increased with increasing sulfurization temperature from 400 to 450 °C and that of the films sulfurized at temperatures higher than 450 °C was ∼2 µm. The preheated film and the films sulfurized at temperatures lower than 400 °C were composed of Cu_{x}S and CZTS. The Cu_{x}S phase was eliminated from the CZTS films by sulfurization at temperatures higher than 500 °C.

H_{2}S Concentration Dependence of Properties of Cu_{2}ZnSnS_{4} Thin Film Prepared under Nonvacuum Condition

Kazuya Maeda, Kunihiko Tanaka, Yuya Nakano, Yuki Fukui, and Hisao Uchiki — 2011-05-20T09:00:00+09:00

Authors: Kazuya Maeda, Kunihiko Tanaka, Yuya Nakano, Yuki Fukui, and Hisao Uchiki
Cu_{2}ZnSnS_{4} (CZTS) thin films were prepared by a sol–gel sulfurization method. Sulfurization was carried out in H_{2}S of various concentrations and the properties of the films were investigated. The CZTS thin films sulfurized at 500 °C for 1 h in 0.5 and 3% H_{2}S atmospheres had large grains compared with the film sulfurized in 1% H_{2}S atmosphere. From the X-ray diffraction analysis, the CZTS thin film sulfurized for 1 h in 0.5% H_{2}S atmosphere included a small amount of Cu_{x}S as a secondary phase. The films sulfurized for 1 h in 1 and 3% H_{2}S atmospheres were composed of a CZTS phase without Cu_{x}S. Owing to the long sulfurization process, the Cu_{x}S phase was eliminated and the optical properties of the films were improved. The size of the grains sulfurized in 1% H_{2}S increased with increasing sulfurization time from 2 to 3 h.

Annealing Effect of Ce-Doped CaGa_{2}S_{4} Synthesized by Mechanochemical Solid-State Reaction

Takumi Ohta, Kunihiko Tanaka, and Hisao Uchiki — 2011-05-20T09:00:00+09:00

Authors: Takumi Ohta, Kunihiko Tanaka, and Hisao Uchiki
The effect of annealing on samples prepared by ball milling of a mixture of CaS, Ga_{2}S_{3}, and Ce_{2}S_{3} powders was investigated. When the mixture of powders was ball-milled for 1 h, no crystalline CaGa_{2}S_{4}:Ce was formed, and by subsequent annealing at 400 °C, CaGa_{2}S_{4}:Ce crystallites were formed. When the mixture powder was ball-milled for 5 h, nanometer-sized CaGa_{2}S_{4}:Ce crystallites were mechanochemically synthesized without heat treatment. By subsequent annealing of the crystallites at several temperatures from 300 to 800 °C, the strain on the mechanochemically synthesized Ce-doped CaGa_{2}S_{4} nanometer-sized crystallites was removed and crystallites of about dozens of nanometer size were retained by 500 to 600 °C annealing.

Growth of γ-In_{2}Se_{3} Thin Films by Electrostatic Spray Pyrolysis Deposition

Takamasa Kato, Toshitaka Hiramatsu, and Norio Onojima — 2011-05-20T09:00:00+09:00

Authors: Takamasa Kato, Toshitaka Hiramatsu, and Norio Onojima
γ-In_{2}Se_{3} thin films were grown by the electrostatic spray pyrolysis deposition growth technique. We investigated the dependence of the crystalline quality and optical properties of the grown films on the growth conditions, such as growth temperatures and the molar ratios of source material Se/In in the precursor solution. The films which were highly aligned to the c-axis were grown at low growth temperature of 250 °C on glass substrates. The optical band gap energy was about 1.94 eV and was independent of the growth temperatures and the molar ratios Se/In in the precursor solution.

Initial Growth Process in Electrochemical Deposition of ZnO

Atsushi Ashida, Naoya Nouzu, and Norifumi Fujimura — 2011-05-20T09:00:00+09:00

Authors: Atsushi Ashida, Naoya Nouzu, and Norifumi Fujimura
ZnO thin films were prepared by electrochemical deposition on (111)Pt/c-sapphire from zinc nitrate aqueous solution by supplying constant current. All films were epitaxially grown, but with a wide distribution of in-plane orientation. For several tens of seconds after the start of the deposition, the time course of cathodic potential showed positive potential versus Ag/AgCl, which is out of range for ZnO growth. Then, the potential decreased abruptly to a negative value and remained constant in the growth range. To evaluate the initial crystal growth, the deposition was stopped immediately after the decrease in potential and the resultant film was characterized by reflective high-energy electron diffraction analysis. The sample was found to contain Zn(OH)_{2}; therefore, the distribution of the in-plane orientation of the ZnO films is considered to arise from this initial growth of Zn(OH)_{2}.

Effects of Ga Doping and Substrate Temperature on Electrical Properties of ZnO Transparent Conducting Films Grown by Plasma-Assisted Deposition

2011-05-20T09:00:00+09:00

Authors: Takashi Matsumoto, Keiichi Mizuguchi, Takahiro Horii, Shiho Sano, Tsutomu Muranaka, Yoichi Nabetani, Satoshi Hiraki, Hideaki Furukawa, Akihiro Fukasawa, Shingo Sakamoto, Shigeru Hagihara, Hiroshi Kono, Kazuhiro Kijima, Osamu Abe, and Kouji Yashiro
Transparent conducting ZnO films are deposited by plasma-assisted deposition on glass and plastic substrates at temperatures as low as 50 °C. The effects of Ga doping and growth temperature on electrical properties are studied using Hall measurement and X-ray diffraction. Carrier density increases with Ga doping for both 50 and 300 °C growth. For low-temperature growth, the carrier mobility in undoped ZnO films is the same as that in high-temperature-grown films, but it becomes lower as the Ga doping level becomes higher. Lattice expansion in both c and a axes directions is observed for low-temperature-grown highly Ga-doped films. The relation between the mobility reduction and the lattice expansion is discussed.

Growth of IrO_{x}–SnO_{x} Films Deposited by Reactive Sputtering

Shun Harada, Kenji Yoshino, Syuji Fukudome, Yoshihiko Kawano, and Fumihiro Sei — 2011-05-20T09:00:00+09:00

Authors: Shun Harada, Kenji Yoshino, Syuji Fukudome, Yoshihiko Kawano, and Fumihiro Sei
IrO_{x}–SnO_{x} thin films were deposited on a glass substrate by reactive sputtering using two types of SnO_{2} and Ir targets between room temperature (RT) and 200 °C. The X-ray diffraction pattern indicates crystallization at 100 °C, and identifies IrO_{x}–SnO_{x} thin films as tetragonal rutile type structures. The IrO_{x}–SnO_{x} thin films also exhibit low average transmittance and resistivity at 100 °C.

Characteristic of Low Resistivity Fluorine-Doped SnO_{2} Thin Films Grown by Spray Pyrolysis

Minoru Oshima and Kenji Yoshino — 2011-05-20T09:00:00+09:00

Authors: Minoru Oshima and Kenji Yoshino
Transparent conducting oxide films of fluorine-doped SnO_{2} (FTO) were deposited on glass substrates by spray pyrolysis in order to determine the effect of spray solution concentration. These films were prepared with different F-doping concentrations from 0 to 33 mol %. The films were all polycrystalline with tetragonal crystal structures. The best electro-optic properties were achieved with a fluorine doping concentration of 17 mol % at a substrate temperature of 500 °C. These conditions resulted in a film with an average transmittance of 82%, a resistivity of 4.0 ×10^{-4} Ω cm, a carrier concentration of 4.7 ×10^{20} cm^{-3} and a mobility of 34 cm^{2} V^{-1} s^{-1}.

Evaluation of Composition Reproducibility of HgCdTe Epitaxial Layers Grown in Novel Liquid Phase Epitaxy Apparatus

Emil Huseynov, Shikhamir Eminov, Alovsat Rajabli, and Tarlan Ibragimov — 2011-05-20T09:00:00+09:00

Authors: Emil Huseynov, Shikhamir Eminov, Alovsat Rajabli, and Tarlan Ibragimov
The results of Hg_{1-x}Cd_{x}Te layer growth by liquid phase epitaxy (LPE) from the Te-rich solution (Hg_{1-z}Cd_{z})_{1-y}Te_{y} with z=0.0545 and y=0.806 obtained by the tipping method in a closed system are presented. The epitaxial layers with different compositions, x=0.20–0.22, and thicknesses ranging from 10 to 20 µm, which are suitable for manufacturing IR photodiode structures, were grown on (111) B-oriented Cd_{0.96}Zn_{0,04}Te substrates at 501–470 °C in a sealed quartz ampoule. A novel LPE apparatus for obtaining of a residual-melt-drop-free surface is described. The effect of the preliminary synthesis of the source on the reproducibility of both the liquidus temperature (ΔΘ±1.8 °C) and epilayer composition (Δx±0.003) was evaluated using the expression for the Hg–Cd–Te phase diagram. As-grown layers exhibit p-type conductivity with a carrier concentration in the range from 4×10^{16} to 1.4×10^{17} cm^{-3} and mobility of 240–270 cm^{2} V^{-1} s^{-1}. The concentration and mobility of charge carriers in the layers annealed at 280 °C for 10 h under Hg overpressure were found to be 5×10^{15} cm^{-3} and 1×10^{4} cm^{2} V^{-1} s^{-1}, respectively.

Time-Resolved Microphotoluminescence Study of Cu(In,Ga)Se_{2}

2011-05-20T09:00:00+09:00

Authors: Takeaki Sakurai, Keiki Taguchi, Muhammad Monirul Islam, Shogo Ishizuka, Akimasa Yamada, Koji Matsubara, Shigeru Niki, and Katsuhiro Akimoto
The carrier recombination processes in Cu(In_{1-x},Ga_{x})Se_{2} (CIGS) thin films were investigated by time-resolved microscopic-photoluminescence (µ-PL) measurement at room temperature. For films with x = 0.45, the spatial distribution of the donor–acceptor pair luminescence is much larger than the grain size. The PL decay lifetime is directly correlated with the µ-PL intensity, but the spectral shape is identical regardless of the sample position. These results suggest that the nonuniform distribution of nonradiative recombination centers mainly affects the carrier recombination in CIGS thin films. At relatively high Ga concentrations (x ≥0.7), the spatial inhomogeneity in µ-PL intensity is enhanced and decay accelerated, suggesting an increase in the density of nonradiative recombination centers. Thus, suppression of nonradiative recombination is critical to enhancing the performance of CIGS-based solar cells.

Photoluminescence of Cu(In,Ga)Se_{2} in the Solar Cell Preparation Process

Sho Shirakata, Shinji Yudate, Jyunji Honda, and Naoki Iwado — 2011-05-20T09:00:00+09:00

Authors: Sho Shirakata, Shinji Yudate, Jyunji Honda, and Naoki Iwado
Room-temperature photoluminescence (PL) has been studied in Cu(In,Ga)Se_{2} (CIGS) films with emphasis on the near-band-edge PL of CIGS during the solar cell fabrication process. A step-by-step PL spectrum mapping measurement was carried out on the following cell processes: depositions of CIGS absorber, CdS buffer, high-resistivity undoped ZnO buffer, and low-resistivity Al-doped window ZnO layers, and the final cell separation process by mechanical scribing. The systematic change in PL intensity during the process has been studied, and the usefulness of PL as a noncontact process monitor has been demonstrated.

Excited States of the A and B Free Excitons in CuInSe_{2}

2011-05-20T09:00:00+09:00

Authors: Michael V. Yakushev, Franziska Luckert, Clement Faugeras, Anatoli V. Karotki, Alexander V. Mudryi, and Robert W. Martin
CuInSe_{2} single crystals, grown by the vertical Bridgman technique were studied using polarisation resolved photoluminescence (PL) at cryogenic temperatures. The emission lines related to the first (n = 2) excited states for the A and B free excitons were observed in the PL spectra at 1.0481 and 1.0516 eV, respectively. The spectral positions of these lines were used to estimate accurate values for the A and B exciton binding energies (8.5 and 8.4 meV, respectively), Bohr radii (7.5 nm), band gaps (E_{g}^{A} = 1.050 eV and E_{g}^{B} = 1.054 eV), and the static dielectric constant (11.3) assuming the hydrogenic model.

Photoluminescence Study of AgInS_{2} by Using Confocal Microscopy System

2011-05-20T09:00:00+09:00

Authors: Umihito Miyamoto, Akinori Sizuki, Kazuhiro Honjo, YongGu Shim, Takahiro Tokuda, Kenji Yoshino, Nazim Mamedov, and Kazuki Wakita
The photoluminescence (PL) spectra of AgInS_{2} crystals grown by a hot-press method have been investigated by confocal microspectroscopy. The two-dimensional image of PL intensity, which shows an area of the chalcopyrite and orthorhombic structures, with a high resolution of micrometer order was obtained. The free-exciton and biexciton emissions on the chalcopyrite structure were clearly separated. Furthermore, the temperature dependence of band-gap energy was analyzed.

Peculiar Linear Dispersive Bands Observed in Angle-Resolved Photoemission Spectra of Tl-Based Ternary Chalcogenide TlGaTe_{2}

2011-05-20T09:00:00+09:00

Authors: Kojiro Mimura, Takahiko Ishizu, Satoru Motonami, Kazuki Wakita, Masashi Arita, Sadig Hamidov, Zakir Chahangirli, Yukihiro Taguchi, Hirofumi Namatame, Masaki Taniguchi, Guseyn Orudzhev, and Nazim Mamedov
Electronic energy bands of the Tl-based ternary chalcogenide TlGaTe_{2} with a quasi one-dimensional crystalline structure have been studied by means of high resolution angle-resolved photoemission spectroscopy (ARPES) in order to check for dispersive structures similar to the Dirac cone observed in the surface bands of Bi-based binary chalcogenides. Two linear dispersive structures which are not reproduced in band calculations for bulk material have been observed in the energy band along the Γ–N direction perpendicular to the chains. These dispersions form a cross-type structure that is centered at the Γ point and extends along the Γ–H–T direction parallel to the chains, reflecting, in our opinion, one-dimensional features of surface morphology of TlGaTe_{2}. The cross-type structure, the energy position of which linearly varies with excitation photon energy, is observed only for high-grade quality surfaces of TlGaTe_{2}. It is therefore assumed that the observed peculiar dispersive structure is caused by the Dirac-type dispersion of high-lying surface conduction bands and that ARPES detects the joint density of states.

Three-Dimensional Atomic Images of TlInSe_{2} Thermoelectric Material Obtained by X-ray Fluorescence Holography

2011-05-20T09:00:00+09:00

Authors: Shinya Hosokawa, Naohisa Happo, Kouichi Hayashi, Kojiro Mimura, Kazuki Wakita, Wen Hu, Hirofumi Ishii, Masato Yoshimura, Jeyaraman Jeyakanthan, and Nazim Mamedov
Three-dimensional (3D) atomic images around the Tl atoms in single-crystal TlInSe_{2} thermoelectric material in the incommensurate phase were reconstructed by Tl L_{III} X-ray fluorescence holography measured at room temperature. In the obtained 3D image, the In atoms are clearly visible at the proper positions in the normal phase. The Tl atomic images are also observed but very weakly. By comparing the experimental image with a theoretically calculated one, it is concluded that only the Tl atoms have large spatial fluctuations, which are related to the incommensurate phase of this material.

Dielectric Anomaly and Conductivity at Ferroelectric Phase Transition in TlInS_{2} Doped with Different Impurities

Oktay Alekperov and Arzu Nadjafov — 2011-05-20T09:00:00+09:00

Authors: Oktay Alekperov and Arzu Nadjafov
The low-frequency dielectric function and conductivity at ferroelectric phase transition have been analyzed in monoclinic TlInS_{2} crystals doped with different impurities. Complementary, room-temperature optical absorption and photoconductivity have been examined to identify shallow and deep energy levels caused by the introduced impurities. It is found that only shallow impurities broaden and shift dielectric anomaly towards lower temperatures. Contrary to our expectation, the dark conductivity at the temperature of the dielectric anomaly is maximum rather than minimum. The dielectric breakdown of the shallow impurities is proposed to be responsible for the observed behavior of the dark conductivity in monoclinic TlInS_{2}.

Photoinduced Current Transient Spectroscopy of TlInS_{2} Layered Crystals Doped with Er, B, and Tb Impurities

2011-05-20T09:00:00+09:00

Authors: MirHasan Yu. Seyidov, Rauf A. Suleymanov, Andrey P. Odrinsky, Arzu I. Nadjafov, Tofig G. Mammadov, and Elnure G. Samadli
Photoinduced current transient spectroscopy (PICTS) has been utilized to study electrically active defects in TlInS_{2} single crystals doped with Er, B, and Tb. Eight traps with activation energies lying in between 0.21 to 0.55 eV have been detected. The origin of these traps is discussed.

Superionic Conductivity in One-Dimensional Nanofibrous TlGaTe_{2} Crystals

2011-05-20T09:00:00+09:00

Authors: Rauf Sardarly, Oktay Samedov, Adil Abdullayev, Famin Salmanov, Andzej Urbanovic, Frédéric Garet, and Jean-Louis Coutaz
We study the temperature dependence of the electrical conductivity σ(T) of TlGaTe_{2} crystals under an electric field (E = 181 V/cm). A strong sharp increase (×1500) in σ(T) is observed at T = 242 K (along the c-axis) and T = 267 K (perpendicular to it). This increase is attributed to a transition towards a superionic conductivity behavior. Over the superionic transition threshold, disordering of the Tl^{+} sublattice in TlGaTe_{2} occurs, and nanoscale topological disordering arises owing to aperiodicity in placing Ga^{3+}Te_{2}^{2-} nanofibers. Terahertz time-domain spectroscopy reveals absorption lines at approximately 0.2 THz that may be attributed to the libration oscillations of the nanofibers.

Synchrotron Radiation Diffraction Study of YbInCu_{4}

2011-05-20T09:00:00+09:00

Authors: Yuki Utsumi, Hitoshi Sato, Chikako Moriyoshi, Yoshihiro Kuroiwa, Hirofumi Namatame, Masaki Taniguchi, Koichi Hiraoka, Kenichi Kojima, and Kunihisa Sugimoto
The structural change of an YbInCu_{4} single crystal has been investigated associated with the first-order valence-transition at T_{V} = 42 K using synchrotron radiation diffraction. The Yb–Cu and In–Cu interatomic distances abruptly increase below T_{V}, following the lattice expansion with no change in the C15b-type crystal structure. We find that the distance between Cu ions forming the Cu_{4} cluster in the crystal is almost unchanged across the valence transition. No abrupt change in the thermal rotational motion of the Cu_{4} cluster is observed at T_{V}.

Local Structure around Mn Atoms in IV–VI Ferromagnetic Semiconductor Ge_{0.6}Mn_{0.4}Te Investigated by X-ray Fluorescence Holography

2011-05-20T09:00:00+09:00

Authors: Naohisa Happo, Yuki Takehara, Makoto Fujiwara, Koichi Tanaka, Shinya Senba, Shinya Hosokawa, Kouichi Hayashi, Wen Hu, Motohiro Suzuki, and Hironori Asada
The local atomic structure around Mn atoms in Ge_{1-x}Mn_{x}Te thin-film single crystal has been investigated by X-ray fluorescence holography (XFH) at room temperature. The obtained atomic image suggests that the Mn atoms replace the Ge atoms in the host GeTe, and the Mn position is stable in the exact positions of the anion fcc sublattice. The XFH result also suggests the fluctuation of the Ge positions or the cation vacancies.

Comparison of Optical Parameters of Ge–As(Sb)–Se(Te) Glassy Films

2011-05-20T09:00:00+09:00

Authors: Eldar Mammadov, Yong-Gu Shim, Junichi Sakamoto, Kazuki Wakita, Nazim Mamedov, and Hisao Uchiki
We compare optical parameters of Ge_{2}As(Sb)_{2}Se(Te)_{x} (x = 5, 7) glassy films. Optical gap obtained from transmission and reflection measurements decreases in the sequence Ge–As–Se → Ge–Sb–Se → Ge–As–Te → Ge–Sb–Te similarly to decreasing glass-forming ability of bulk systems. We have found from spectroscopic ellipsometry measurements that spectral dependence of imaginary part of the dielectric function shifts to lower energies in the same sequence. This indicates to strong correlation between structural arrangement of atoms in these ternaries and their electronic properties. Ge_{2}Sb_{2}Se_{5} crystallizes upon thermal annealing with accompanying change in reflectivity. No change in the structure of Ge_{2}As_{2}Se_{5} is found after annealing.

Optical and Structural Properties of Zn–Cd–Mn–Se Double Quantum Well Systems

2011-05-20T09:00:00+09:00

Authors: Takashi Matsumoto, Kenta Ohmori, Kazuki Kodama, Masao Hishikawa, Sakyo Fukasawa, Fumiaki Iwasaki, Tsutomu Muranaka, and Yoichi Nabetani
Double quantum well (DQW) structures consisting of a ZnCdSe well and a ZnCdMnSe well separated by a ZnSe barrier are grown with molecular beam epitaxy (MBE). The DQW structures are characterized by using X-ray diffraction measurement and simulation. Thickness of each well layer is designed so that the lowest energy level of ZnCdMnSe well is close to the excited level of the ZnCdSe well. Optical properties of the DQWs are studied with photoluminescence (PL) and reflection spectra in external magnetic fields up to 8 T in the Faraday geometry. Exciton transfer from ZnCdMnSe well to ZnCdSe well is observed in magneto PL with energy selective photoexcitation. Exciton energies in ground and excited states are estimated from PL excitation spectra and reflection spectra.

Spectroscopic Ellipsometry Studies of CdS:O Layers for Solar Cells

2011-05-20T09:00:00+09:00

Authors: Yong-Gu Shim, Junichi Sakamoto, Akinori Suzuki, Khuraman Khalilova, Kazuki Wakita, Nazim Mamedov, Ayaz Bayramov, Emil Huseynov, and Ilham Hasanov
This work reports the results of spectroscopic ellipsometry study of CdS thin films, deposited on glass substrates in the presence of oxygen at room temperature by rf sputtering. The data acquisition, together with the subsequent linear regression analysis to restore dielectric function has been performed over the photon energy range 1.5–5.0 eV. The obtained oxygen-free CdS films and reference bulk CdS have been found to be very much the same regarding their dielectric function spectra. On the other hand, blue-shift of the main structures in dielectric function has been observed for CdS:O films deposited at 5% value of O/Ar ratio. In spite of the broadening taking place on a par with the shift, the last turns out to be so large that provides transparency of CdS:O thin films in a spectral range above the energy gap of CdS. The obtained results allow to considering CdS:O as an improved window-layer material for solar cell application.

High-Pressure Studies for Iron-Based Superconductors

2011-05-20T09:00:00+09:00

Authors: Hiroki Takahashi, Hiroyuki Takahashi, Takahiro Tomita, Hironari Okada, Yoshikazu Mizuguchi, Yoshihiko Takano, Satoru Matsuishi, Masahiro Hirano, and Hideo Hosono
Electrical and magnetic measurements for 1111 type Ca(Fe_{1-x}Co_{x})AsF and 11 type Fe(Se_{1-x}Te_{x}) have been performed under high pressure. Superconductivity appeared with Co substitution for Ca(Fe_{1-x}Co_{x})AsF. For superconducting Ca(Fe_{1-x}Co_{x})AsF, pressure does not enhance the superconductivity so much. Disorder induced by the Co substitution in the FeAs superconducting layer is considered to be related to the pressure dependence of T_{c}. Pressure-induced superconductivity was observed for x = 0.0 and 0.05. For Fe(Se_{1-x}Te_{x}), T_{c} exhibits the maximum value at x = 0.5 and decreases with increasing Te concentration. The enhancement of T_{c} with pressure was suppressed by increasing Te concentration for Fe(Se_{1-x}Te_{x}) (x ≧0.5). For non-superconducting FeTe, pressure-induced superconductivity was not detected under high pressure up to 19 GPa.

Anomalies in Transport and Superconducting Properties of Ba_{1-x}K_{x}Fe_{2}As_{2} Single Crystals

2011-05-20T09:00:00+09:00

Authors: Vladimir N. Zverev, Alexey V. Korobenko, Guoli L. Sun, Dunlu L. Sun, Chengtian T. Lin, and Alexander V. Boris
The transport and superconducting properties of Ba_{1-x}K_{x}Fe_{2}As_{2} single crystals were studied. Both in-plane and out-of-plane resistivity were measured by Montgomery method. The in-plain resistivity temperature dependence was found to be nonlinear with the tendency to saturate at high temperature. We have found that the resistivity anisotropy is almost independent of temperature and lies in the range 10–40 for the studied samples. We explain this result by the extrinsic nature of high out-of-plane resistivity, which may be due to the presence of flat defects along Fe–As layers. This statement is supported by comparatively small effective mass anisotropy, obtained from the upper critical field measurements.

Temperature-Induced Valence Transition of EuPd_{2}Si_{2} Studied by Hard X-ray Photoelectron Spectroscopy

2011-05-20T09:00:00+09:00

Authors: Kojiro Mimura, Takayuki Uozumi, Takahiko Ishizu, Satoru Motonami, Hitoshi Sato, Yuki Utsumi, Shigenori Ueda, Akihiro Mitsuda, Kenya Shimada, Yukihiro Taguchi, Yoshiyuki Yamashita, Hideki Yoshikawa, Hirofumi Namatame, Masaki Taniguchi, and Keisuke Kobayashi
We have studied the electronic structure of EuPd_{2}Si_{2} by hard X-ray photoelectron spectroscopy (HX-PES) from 300 to 20 K. The temperature-dependent HX-PES spectra clearly show the valence transition, namely, the intensities of the divalent and trivalent Eu 3d components are abruptly changed. The change in Eu 3d spectral shape, especially the drastic change in the trivalent Eu 3d feature with temperature, can be explained within the framework of the Anderson model. The peak shift of Pd 3d core level with temperature indicates that the valence electrons of Pd contribute to the temperature-induced valence transition of EuPd_{2}Si_{2}.

Metal–Insulator Transition Induced by Temperature in Bi_{2}Te_{3-x}Cl_{x} Layered Compound

2011-05-20T09:00:00+09:00

Authors: Nadir A. Abdullayev, Nadir M. Abdullayev, Xayala V. Aliguliyeva, Samir Sh. Gahramanov, Taira G. Kerimova, Konul M. Mustafayeva, Sergey A. Nemov, and Vladimir N. Zverev
It is shown, that doping by chlorine atoms changes the type of conductivity of Bi_{2}Te_{3} from p- to n-type as well as the character of conductivity. In the direction perpendicular to the layers plane phonon assisted hopping conductivity is observed. The mechanism of charge transport in Bi_{2}Te_{3} crystals doped by chlorine atoms is proposed.

γ-Radiation Stimulated Structural Transition of Monoclinic TlInS_{2} to Hexagonal Phase

Oktay Alekperov, Nazim Mamedov, Nuru Safarov, Vagif Gasumov, and Arzu Nadjafov — 2011-05-20T09:00:00+09:00

Authors: Oktay Alekperov, Nazim Mamedov, Nuru Safarov, Vagif Gasumov, and Arzu Nadjafov
Temperature dependent dielectric function and conductivity, as well as room temperature photoconductivity have been investigated on monoclinic TlInS_{2} subjected to γ-radiation in a wide range of radiation doses. The structural changes have been detected by XRD performed after every stage of γ-irradiation. Frenkel pairs (vacancies and interstitial sulfur atoms) have been assumed to appear in TlInS_{2} at irradiation doses below 100 Mrad through well-known Klinger's “residual charged impurity assisted electrostatic” mechanism. These defects eventually lead to the formation of neutral impurity complexes responsible for the observed sharpening of the anomalies in dielectric function and conductivity at the temperature of the well-known ferroelectric phase transition in TlInS_{2}. The last anomalies become smeared out at irradiation doses above 200 Mrad. Finally, the transformation of the monoclinic TlInS_{2} to the one with hexagonal structure has been witnessed in a thin surface layer at high fluencies (1000–1500 Mrad) of γ-radiation.

The Role of Electronic Subsystem in the Negative Thermal Expansion of Ferroelectric–Semiconductor TlGaSe_{2}

2011-05-20T09:00:00+09:00

Authors: Tofig G. Mammadov, Nadir A. Abdullayev, MirHasan Yu. Seyidov, Rauf A. Suleymanov, and Emin Yakar
Effect of illumination and external electric field on thermal expansion of TlGaSe_{2} crystals has been investigated. Strong transformation of negative linear expansion coefficient has been observed. It is supposed that two main mechanisms are responsible for observed effects: formation of electret state and reverse piezoelectric effect. The electronic nature of negative linear expansion of TlGaSe_{2} crystals has been proved for the first time.

Charged Defects as an Origin of the Memory Effect in Incommensurate Phase of TlInS_{2} Ferroelectric–Semiconductors

2011-05-20T09:00:00+09:00

Authors: MirHasan Yu. Seyidov, Rauf A. Suleymanov, Tofig G. Mammadov, Aleksandr K. Fedotov, Sardar S. Babayev, and Galib M. Sharifov
The effects of annealing within the incommensurate phase and doping with the lanthanum impurity on the dielectric function ε of the TlInS_{2} single crystals have been investigated. It is shown that illumination and application of external electric field transform the ε(T) dependences for both the annealed and doped samples in the same manner. The inference is made that the correlation between observed effects is conditioned by the internal electric fields induced either by activation (polarization) of native defects during the annealing procedure or after the doping the crystals with active La centers.

Ab initio Calculations of Elastic Constants of Superalloys

Eyvaz I. Isaev, Alena V. Ponomareva, Ivan D. Bleskov, and Yuri Kh. Vekilov — 2011-05-20T09:00:00+09:00

Authors: Eyvaz I. Isaev, Alena V. Ponomareva, Ivan D. Bleskov, and Yuri Kh. Vekilov
Using the-state-of-the-art ab initio method we have studied elastic constants of alloys potentially interesting for high temperature applications. We have shown that Cr substitutes the Al sublattice in B2 NiAl at concentration up to 40 at. %, but at higher Cr content it prefers the Ni-sublattice. Alloying of NiAl with Cr yields reduced strength but improves the ductility of the alloys. Alloying of NiAl with W which substitutes the Al sublattice, leads to a strong decrease of the shear modulus, and near 50 at. % of W the alloy becomes mechanically unstable as elastic constant C' is negative. This is in agreement with our phonon calculations where we found soft modes along the [110] direction for B2 NiW. According to our calculations in (Ru,Ni)Al alloys the shear modulus is almost constant up to 40 at. % of Ni, at higher Ni concentrations it is drastically reduced. We have shown that the changes in elastic properties of (Ru–X)Al alloys are due to electronic topological transitions.

The Phonon Percolation Scheme for Alloys: Extension to the Entire Lattice Dynamics and Pressure Dependence

2011-05-20T09:00:00+09:00

Authors: Gopal Krushna Pradhan, Chandrabhas Narayana, Mala Narasappaya Rao, Matteo D’Astuto, Samrath Lal Chaplot, Olivier Pagès, A. Breidi, Jihane Souhabi, Andrei Postnikov, Sudip Kumar Deb, Tapas Ganguli, Alain Polian, Gopalkrishna Bhalerao, Abhay Shukla, Franciszek Firszt, and Wojciech Paszkowicz
We explore two basic issues behind the 1-bond → 2-mode percolation scheme that has recently lead to a unification of the classification of the Raman and infrared spectra of usual zincblende semiconductor alloys. In doing so we focus on the model ZnBeSe alloy, for which the percolation scheme was originally developed. First, we show by using inelastic neutron scattering that the well-resolved 1-bond → 2-mode percolation doublet of the short Be–Se bond detected close to the zone center by Raman and infrared spectra remains observable throughout the whole Brillouin zone up to the zone edge. This testifies for an origin at the bond scale. Second, high-pressure is used to disable a Fano interference which screens the Zn–Se Raman signal, revealing a distinct Zn–Se percolation doublet. This provides experimental evidence that the 1-bond → 2-mode percolation scheme is generic, and may, in principle, apply to all bonds in an alloy.

Spin–Orbit Interactions in a Quasi-Two-Dimensional Electron Gas with Finite Thickness

Enver Nakhmedov, Oktay Alekperov, and Reinhold Oppermann — 2011-05-20T09:00:00+09:00

Authors: Enver Nakhmedov, Oktay Alekperov, and Reinhold Oppermann
Effects of the spin–orbit coupling on the energy spectrum, Fermi surface and spin dynamics are studied in structural- and bulk-inversion asymmetric quasi-two-dimensional structures with a finite thickness in the presence of a parabolic transverse confining potential. One-particle quantum mechanical problem in the presence of an in-plane magnetic field is solved numerically exact. Interplay of the spin–orbit interactions, orbital- and Zeeman-effects of the in-plane magnetic field results in a formation of a multi-valley subband structure, typical for realization of the Gunn effect. A possible Gunn-effect-mediated spin accumulation is discussed. The spin–orbit interactions and in-plane magnetic field are shown to change the regular plateau structure of the ballistic conductance.

Ab initio Phonons in Kesterite and Stannite-Type Cu_{2}ZnSnSe_{4}

Andrei Postnikov and Narjes Beigom Mortazavi Amiri — 2011-05-20T09:00:00+09:00

Authors: Andrei Postnikov and Narjes Beigom Mortazavi Amiri
On the basis of density functional calculations of electronic structure by the Siesta method in the local density approximation, the zone-center vibrational spectra for two crystallographic modifications of Cu_{2}ZnSnSe_{4} are constructed. The difference of frequencies, between kesterite and stannite phases, of some characteristic modes is discussed. It is suggested to use some of these modes (notably the Zn-related one at 239–254 cm^{-1}) as a vibrational signature of the kesterite structure, e.g., for samples characterization.

Ab initio Lattice Dynamics and Grüneisen Parameters of TlGaSe_{2}

2011-05-20T09:00:00+09:00

Authors: Dilara A. Huseinova, Firudin M. Hashimzade, Guseyin S. Orudzhev, Munira A. Nizametdinova, and Kerim R. Allakhverdiev
The first-principles calculations of the lattice dynamics of the TlGaSe_{2} ternary semiconductor compound are presented in this paper. Calculations were performed using open-source code ABINIT on the basis of the density functional perturbation theory within the plane-wave pseudopotential approach. Results on the frequencies of phonon modes in the centre of Brillouin zone and the dispersion of transverse shear acoustic branch of the phonon spectra agree well with experimental data on Raman scattering, infrared reflectivity and ultrasound wave propagation in TlGaSe_{2}. The calculated and experimental temperature dependencies of heat capacity are in a good agreement up to the room temperature. Along the layer, the low-frequency acoustic branch displays the bending wave behavior which is characteristic of the layer crystal structures. We have calculated also the elastic compliances tensor, the directional Grüneisen functions and the coefficients of the linear thermal expansion for TlGaSe_{2}. We obtained that both principal components of the coefficients of linear expansion are positive in the range of temperature above 5 K.

Structural, Optical, and Electrical Properties of Semiconductor Compounds Studied by Means of Inelastic Light Scattering from Phonon, Electron, and Coupled Electron–Phonon Excitations: From Bulk to Nanoscale Structures

Farid H. Bayramov, Gert Irmer, Vladimir V. Toporov, and Bakhysh H. Bairamov — 2011-05-20T09:00:00+09:00

Authors: Farid H. Bayramov, Gert Irmer, Vladimir V. Toporov, and Bakhysh H. Bairamov
We show results of our systematic investigation by means of quasi-elastic and inelastic laser light scattering (QEILS) of electron- and hole–phonon interactions as well as charge- and spin-density scattering mechanisms from hole gas fluctuations including their overlapping with phonon features by using near infrared excitation of doped bulk p-GaAs and self-assembled InAs/GaAs quantum dot (QD) structures. Additionally, results of our study of CdS and CdSe/ZnS QDs, multi-functionalized by peptides possessing strict affinity to integrins of MDA-MB-435 cancer cells are also presented.

Ab initio Phonons in Magnetic Ni_{2}MnAl

Leyla Isaeva, Dmitry Bazhanov, Eyvaz Isaev, and Olle Eriksson — 2011-05-20T09:00:00+09:00

Authors: Leyla Isaeva, Dmitry Bazhanov, Eyvaz Isaev, and Olle Eriksson
In the present work we report the results of ab initio studies of electronic and dynamic properties of nickel based Heusler alloy Ni_{2}MnAl. The total magnetic moment and elastic constants were also evaluated and compared to experimental results where possible. We found that the phonon dispersion relations calculated in this work within the linear response method did not reveal any softening of the transversal acoustic mode TA_{2} along [ξ, ξ, 0] direction in accordance with the experiment and in controversy to previous theoretical studies.

Multiscale Simulation of Nanostructured Materials and Systems

2011-05-20T09:00:00+09:00

Authors: Vladislav Nelayev, Viatcheslav Barkaline, Teodor Brechko, Alexander Chashynski, Viachaslau Lyskovski, and Nazim Mamedov
A hierarchical approach to simulation of nanostructured materials and systems is discussed by examples of ab initio calculations of the strain dependence of electronic properties of TlMeX_{2} compounds (Me = In, Ga, Tl; X = S, Se, Te) and study of sensitivity of ordered carbon nanotube (CNT) array based acoustic gas sensors.

Influence of Exchange Interaction on Phonon–Polaron Properties in Diluted Magnetic Semiconductors

Seyid-Nisa M. Seyid-Rzayeva — 2011-05-20T09:00:00+09:00

Authors: Seyid-Nisa M. Seyid-Rzayeva
The energy spectrum of a phonon–polaron effect with weak coupling has been obtained in the classical magnetic field for diluted magnetic semiconductors, which has a cubic crystal structure with a one-valley anisotropic energy spectrum of the band electrons. Analytical expressions for polaron binding energy and lowest polaron subband energy (i.e., polaron ground-state energy of the lowest conduction subband with spin ↓), and the transverse and longitudinal polaron effective masses of the electron in the dependence on the magnetic field were found. On the basis of quantitative calculations, it has been established that with increasing magnetic field, polaron binding energy is decreased owing to the exchange interaction. Also, it has been established that the lowest polaron subband energy is shifted down in energy; at the same time, the bottom of the lowest polaron subband energy is located much lower compared with the bottom of the polaron band for the standard spectrum.

Entropy of Superlattices in a Quantized Magnetic Field

Bahram M. Askerov, Sophia R. Figarova, Mehdi M. Mahmudov, and Vagif R. Figarov — 2011-05-20T09:00:00+09:00

Authors: Bahram M. Askerov, Sophia R. Figarova, Mehdi M. Mahmudov, and Vagif R. Figarov
The entropy of a degenerate and a nondegenerate low dimensional electron gas in a quantized magnetic field is calculated. It is noted the entropy of a two-dimensional electron gas essentially exceeds entropy of three-dimensional electron gas. It is shown the entropy of a degenerate quasi-two-dimensional electron gas is directly proportional to the state density. The ratio of entropy of a degenerate two-dimensional electron gas to entropy of three-dimensional electron gas in the quantum limit is determined by the ratio of effective masses across and along layers.

Phase Stability and Electronic Structure of In-Free Photovoltaic Materials Cu_{2}IISnSe_{4} (II: Zn, Cd, Hg)

Satoshi Nakamura, Tsuyoshi Maeda, and Takahiro Wada — 2011-05-20T09:00:00+09:00

Authors: Satoshi Nakamura, Tsuyoshi Maeda, and Takahiro Wada
We have theoretically evaluated the phase stability and electronic structure of Cu_{2}CdSnSe_{4} and Cu_{2}HgSnSe_{4} and compared the results with those of Cu_{2}ZnSnSe_{4}. The enthalpies of formation for kesterite (KS), stannite (ST), and wurtz-stannite (WST) phases of Cu_{2}ZnSnSe_{4} (CZTSe), Cu_{2}CdSnSe_{4}, and Cu_{2}HgSnSe_{4} were calculated by first-principles calculations. In Cu_{2}CdSnSe_{4} and Cu_{2}HgSnSe_{4}, the stannite (ST) phase is the most stable among these phases. The valence band maximum (VBM) of ST-type Cu_{2}CdSnSe_{4} consists of antibonding orbitals of Cu 3d and Se 4p, while the conduction band minimum (CBM) consists of antibonding orbitals of Sn 5s and Se 4p. The VBM of Cu_{2}HgSnSe_{4} also consist of antibonding orbitals of Cu 3d and Se 4p. However, the CBM of Cu_{2}HgSnSe_{4} consists of antibonding orbitals of Hg 6s, Sn 5s, and Se 4p.

Effect of Rare Earth Element Codoping on the Mn Red Emission in Ca and Sr Thiogallates: Focusing on Its Mechanism through Electron Spin Resonance Study of Single Crystals

Takeo Takizawa, Toshimitsu Obonai, Shigetaka Nomura, and Chiharu Hidaka — 2011-05-20T09:00:00+09:00

Authors: Takeo Takizawa, Toshimitsu Obonai, Shigetaka Nomura, and Chiharu Hidaka
The weak Mn^{2+} involved red emission in CaGa_{2}S_{4} can be greatly enhanced by codoping with a suitable rare earth element (REE). To clarify the involved physical mechanism, the actual Mn sites in the host crystal are investigated through electron spin resonance (ESR) measurements of single crystals. Three different patterns of ESR signals with different angular dependences are observed by rotating the magnetic field around the three crystal axes. As a result, three independent sites occupied by the Mn^{2+} ions are confirmed. Based on the experimental finding that the hyper fine constants (HFS) for the three sites are nearly the same, the Mn^{2+} ion sites may be ascribed to the Ca or Ga sites. To finally solve this ascription issue, ESR measurements of Eu^{2+} in CaGa_{2}S_{4} are carried out, where the Eu^{2+} ions have been shown to exclusively substitute at Ca sites. From the similar angular variation of the ESR signals of Eu^{2+} and Mn^{2+}, the Mn substitutional sites are finally determined to be the three Ca ones. A broad ESR signal appearing in the vicinity of the Lande g factor (g = 2.0) suggests the possible presence of Mn clusters. We have to investigate to see whether these may be the actual emission centers.

Luminescence Properties of Barium Thio- and Selenogallates Doped with Eu, Ce, and Eu+Ce

2011-05-20T09:00:00+09:00

Authors: Gennadii P. Yablonskii, Vitaly Z. Zubialevich, Eugenii V. Lutsenko, Arif M. Pashaev, Bahadir G. Tagiev, Oktay B. Tagiev, and Said A. Abushov
Photoluminescence properties of barium thio- and selenogallates doped with Eu^{2+}, Ce^{3+} and co-doped with Eu^{2+} and Ce^{3+} were studied in a temperature range of 10–300 K and an optical excitation intensity interval of 3×10^{-4}–1.25×10^{6} W/cm^{2}. Barium thiogallates doped with europium and co-doped by both rare-earth elements show a high thermal stability of the luminescence characteristics and significantly exceed the selenogallate analogues in respect of photoluminescence efficiency. Both thio- and selenogallates activated with the rare-earth elements demonstrate a considerable PL efficiency droop only at high excitation levels exceeding 20 and 10 kW/cm^{2}, respectively. Possible reasons of the droop mechanisms are discussed.

Analysis of the Enhancing Effect of Rare Earth Ion Co-Doping on the Red Emission of CaGa_{2}S_{4}:Mn^{2+} in View of Its Decay Time

Akihiro Suzuki, Chiharu Hidaka, Takeo Takizawa, and Shigetaka Nomura — 2011-05-20T09:00:00+09:00

Authors: Akihiro Suzuki, Chiharu Hidaka, Takeo Takizawa, and Shigetaka Nomura
When certain trivalent rare earth elements (REEs) are co-doped with Mn^{2+} in CaGa_{2}S_{4}, the Mn^{2+} red emission of the compounds is enhanced. To clarify its mechanism, its decay curves of the Mn^{2+} red emission from CaGa_{2}S_{4}:Mn^{2+}, REE^{3+} are investigated. For these analyses, we present a tentative transition model including the trap levels due to REE^{3+} together with a process enabling electron supply from REE^{3+} to the excited 3d state of Mn^{2+}. This model can explain the enhancing effect on the Mn^{2+} red emission.

Effect of Ho Co-Doping on the Long Lasting Emission of CaGa_{2}S_{4}:Eu

Chiharu Hidaka and Takeo Takizawa — 2011-05-20T09:00:00+09:00

Authors: Chiharu Hidaka and Takeo Takizawa
To investigate the long-lasting green afterglow from Ho added CaGa_{2}S_{4}:Eu compounds, photoluminescence (PL) and photoluminescence excitation (PLE) spectra are measured as a function of Ho concentration by keeping Eu one at 0.1 and 0.5 mol %. As Ho concentration increases, PL intensity of Eu decreases. PL from Ho at 660 nm has an additional broad excitation band ranging from 400 to 500 nm, emerging only if Eu^{2+} ion is co-doped. Since this new band just coincides with the Eu^{2+} emission in energy, electrons excited to the 5d states of Eu^{2+} are considered to transfer to the Ho excited states, which are actually confirmed by the weakened Eu emission observed. In the decay curve of Eu emission in a co-doped sample, two long-lasting components are observed. Their lifetimes, however, steeply decrease when Ho concentration increases more than 1 mol %. In this paper, energy transfer between the two dopants is discussed.

Switching of Multiples Solitons in Arrays of Coupled Cavities

Keivan M. Aghdami, Reza Kheradmand, and Roghayyeh Karimi — 2011-05-20T09:00:00+09:00

Authors: Keivan M. Aghdami, Reza Kheradmand, and Roghayyeh Karimi
In this paper, light propagation dynamics in a coupled optical cavities array in self-defocusing configuration which has been driven by a holding beam is investigated numerically. It was shown that superposition of appropriate Gaussian control beam and plane wave holding beam can be used to write and erase of discrete cavity solitons and to switch between different orders of solitons. This method develops as an important issue of light control and all optical switches.

Control of Self-Focusing and Self-Defocusing in the Waveguides Array

Keivan M. Aghdami, Abdolrasoul Gharaati, and Fatemeh Mokhtari — 2011-05-20T09:00:00+09:00

Authors: Keivan M. Aghdami, Abdolrasoul Gharaati, and Fatemeh Mokhtari
In this paper, propagation of a Gaussian beam through a one-dimensional array of optically coupled waveguides is investigated using numerical simulation. The results show that the propagation of light is strongly depended on the phase difference of the beams on the entrance face of waveguides. Also, the effect of nonlinear Kerr phenomenon is investigated in such media. Considering this effect, sometimes the slope of divergence is reduced in beam which is occurred because of diffraction, but sometimes depends on initial tilt of the beam, which exhibits an increase in divergence.

Switching On/Off of Cavity Solitons in Semiconductor Microresonators via Carrier Injection above Laser Threshold

Reza Kheradmand and Mansour Eslami — 2011-05-20T09:00:00+09:00

Authors: Reza Kheradmand and Mansour Eslami
We studied the cavity solitons (CSs) and their switching in a semiconductor Fabry–Perot type microresonator where the active medium is multiple quantum well nanostructures. We take benefit of the full set of Maxwell–Bloch equations to describe the dynamical behavior of the system, since the rate equation model for a two-level system fails to explain the system when considering femtosecond time scales. Numerical simulations imply formation of stable CSs which is done by local carrier injection as the switching method. To switch off these CSs we used the same method but with negative amplitude of the injection function. It is also realized that the successive switching on/off of CSs by such a scheme is possible in this system.

Controlling and Stabilizing of Thermally Travelling Optical Structures in Semiconductor Microresonators

Reza Kheradmand and Najmeh Montazeri — 2011-05-20T09:00:00+09:00

Authors: Reza Kheradmand and Najmeh Montazeri
In this paper, controlling and stabilizing the thermally travelling patterns in a semiconductor multiple quantum-well microresonator that driven by a coherent holding beam has been studied. The presence of thermal effects introduces a Hopf instability which in certain regions of the parameter space dominates the dynamics of the system. The oscillatory instabilities can develop a modulational character, meaning that travelling patterns can be found. These phenomena develop over the slow timescale (microseconds) characterizing thermal effects in the devices. We investigated a method for stabilizing and switching the travelling patterns by using spatial perturbation, which can be used as an all optical switch.

Effect of “CdCl_{2} Treatment” on Properties of CdTe-Based Solar Cells Prepared by Physical Vapor Deposition and Close-Spaced Sublimation Methods

2011-05-20T09:00:00+09:00

Authors: Rashad Hajimammadov, Nasser Fathi, Ayaz Bayramov, Genady Khrypunov, Nataliya Klochko, and Tatyana Li
CdTe is regarded as one of the most promising materials for fabricating CdTe/CdS thin film solar cells with efficiencies up to 16.5%. In this paper we present a comparative analysis of CdTe-based solar cells fabricated by physical vapor deposition (PVD) and close-spaced sublimation (CSS) methods. The structural properties of CdTe base layers and the output parameters of CdS/CdTe solar cells are presented, and the influence of “CdCl_{2}-treatment” on these properties are discussed. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were used in the studies.

Peculiarities of Current–Voltage Characteristics of Al–p-Cd_{x}Hg_{1-x}Te Tunnel Metal–Insulator–Semiconductor Structure

Emil Huseynov and Namig Ismayilov — 2011-05-20T09:00:00+09:00

Authors: Emil Huseynov and Namig Ismayilov
The results of current–voltage (I–V) and capacity–voltage (C–V) characterization and study of kinetics of photocurrent relaxation in Al–p-Cd_{x}Hg_{1-x}Te structures with tunnel thin insulating layer at 80 K are presented. All observed qualitative peculiarities are well explained by a simple model, taking into account the relative contribution of recombination of the photogenerated charge carriers and their tunneling through dielectric gap at reverse bias voltage. It is established that the studied structures are suitable for IR-system applications.

Sulfurization Growth of SnS Thin Films and Experimental Determination of Valence Band Discontinuity for SnS-Related Solar Cells

2011-05-20T09:00:00+09:00

Authors: Mutsumi Sugiyama, Yoshitsuna Murata, Tsubasa Shimizu, Kottadi Ramya, Chinna Venkataiah, Tomoaki Sato, and K. T. Ramakrishna Reddy
Tin sulphide is considered to be a potential candidate for the development of low cost polycrystalline thin film solar cells. The advantages of using sulfurization process to grow SnS films were demonstrated. Polycrystalline p-type SnS films were obtained by a simple dry process at 300 °C for 90 min. The sulfurization condition depends on the deposition method of the Sn precursor. Using single-phase SnS films, band discontinuities at SnS/CdS and SnO_{2}/SnS heterointerfaces were measured by X-ray photoelectron spectroscopy. The valence band offsets were determined to be approximately 1.5 eV for SnS/CdS and 3.5 eV for SnO_{2}/SnS interfaces. Using these values and the energy band gaps of the corresponding layers, the energy band diagram was developed. It indicated that the SnS/CdS heterojunction is of TYPE-II form of heterostructure. This result indicated that SnS-related solar cells with CdS as window layer do not have an ideal band structure that could give high conversion efficiency.

Single-Phase Cadmium Telluride Thin Films Deposited by Electroless Electrodeposition

2011-05-20T09:00:00+09:00

Authors: Gennadiy Khrypunov, Natalja Klochko, Neonila Volkova, Viktor Lyubov, and Tatyana Li
By means of analysis of electrochemical processes taking place during electroless electrodeposition have elaborate method for obtaining of well adherent smooth and stoichiometric single-phase CdTe films with cubic structure. Illumination of the growing layers has increased their thickness and improved film crystallinity. Following improvement of CdTe structure was riched by “chloride treatment” of the films. So, the novel electroless electrodeposition technique gives possibilities for the manufacture of CdTe absorbers suitable for η-solar cells.

Reflectance Profile of BaTiO_{3} on Multilayer Antireflection Coating Systems

Filiz Karaomerlioglu — 2011-05-20T09:00:00+09:00

Authors: Filiz Karaomerlioglu
Antireflection (AR) coating systems are very important technology for optoelectronic devices. The optical characteristics of the system can be regulated by external electric or thermal field, and designed broadband ultra low reflection coating systems. It is investigated optical properties of multilayer AR coatings based on different ferroelectric materials to reduce reflectance in other studies. In this study, reflectance profile of BaTiO_{3} on multilayer AR coating systems has been developed in the visible region. It has been used ZnSe and ZrO_{2} as multilayer AR coatings, and BaTiO_{3} as the substrate. Fortran program has been simulated on Fresnell equations base.

Comparison of the Valence Band Structure Peculiarities in the Bi_{0.84}–Sb_{0.16}–Sn_{0.1} and Pure Semiconducting Bi_{1-x}Sb_{x} Alloys

Bakir Tairov and Eltaj Yuzbashov — 2011-05-20T09:00:00+09:00

Authors: Bakir Tairov and Eltaj Yuzbashov
On the basis of measured low magnetic field galvanomagnetic coefficients both for Sn-doped Bi_{0.84}–Sb_{0.16}–Sn_{0.1} and pure semiconducting Bi–Sb alloys, kinetic parameters of the investigated materials have been determined. It is shown that hole ellipsoids corresponding to the obtained results are less anisotropic (ν_{2}/ν_{1} = 0.05, ν_{3}/ν_{1} = 0.5) in comparison with L-hole ellipsoids, where ν_{2}/ν_{1} = 0.009, ν_{3}/ν_{1} = 0.7 and their slope is significantly larger (φ_{h} = 16°) than L-hole (and L-electron) ones. Therefore peculiarities of the valence band for the Bi_{0.84}–Sb_{0.16} alloy and other semiconducting alloys with high content of antimony can not be adequately described by involving dominant contribution of the hole valleys localized in T, H, and L points of the Brioullin zone.

Recent articles in Jpn. J. Appl. Phys.

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Room-Temperature Ferromagnetism in (Zn,Mn,Sn)As_{2} Thin Films Applicable to InP-Based Spintronic Devices

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Peculiarities of Linear Thermal Expansion of CuInS_{2} Single Crystals

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H_{2}S Concentration Dependence of Properties of Cu_{2}ZnSnS_{4} Thin Film Prepared under Nonvacuum Condition

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Excited States of the A and B Free Excitons in CuInSe_{2}

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