bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Cr-Doped CdGeAs2 Using Thermal Admittance Spectroscopy
Authors: Smith S.R. , Evwaraye A.O. , Ohmer M.C. , Saxler A. W. , Goldstein J. T. , Solomona J. , Schunemann P. G. , Pollak T. M. 
Published: April 2011

AbstractThe optical and electrical properties of chrome-doped CdGeAs2 (CGA), an important non-linear optical material, are reported. CGA, a chalcopyrite semiconductor of the pseudo- III-V type, is a close ternary analog to GaAs, possessing significant differences. To date, the electrical and optical properties of as-grown undoped CGA have been controlled by a somewhat shallow dominant residual acceptor which it is the source of significant undesirable optical absorption. Highly transparent semi-insulating CGA should be attainable using compensation and counterdoping schemes similar to those used for GaAs. However, identifying suitable deep and shallow n-type and p-type dopants will require extensive empirical studies. As a starting point of survey to find deep levels, the properties of CGA:Cr have been investigated. Cr is a reasonable choice as it has been used extensively to provide a deep level in GaAs. Thermal Admittance Spectroscopy was used to examine the electrically active levels in this material. These measurements were correlated with temperature dependent Hall effect measurements, and IR absorption measurements. SIMS analysis was utilized to estimate the Cr concentration as the segregation coefficient for Cr in CGA has not been reported.. The results show that there is a p-type level introduced into the band gap at about 0.16 eV above the valence band, a value nominally 50% deeper than that of the native acceptor. The background doping as measured by Capacitance-Voltage measurements was determined to be 8 × 1016 cm−3 near the surface, and 1.0 × 1017 cm−3 in the bulk. These results are compared to similar measurements in undoped material.
Influence of SiOx Capping Layer Quality on Impurity-Free Interdiffusion in GaAs/AlGaAs Quantum Wells
Authors: Deenapanray P.N.K. , Tan H.H. , Jagadish C. 
Published: April 2011

AbstractWe have investigated the influence of SiOx capping layer quality on impurity-free vacancy interdiffusion in GaAs/Al0.54Ga0.46As quantum wells. Dielectric layers were deposited by plasmaenhanced chemical vapor deposition, and properties of layers were changed by varying either the flow rate of silane or deposition temperature. The extent of intermixing in our samples is discussed in terms of the 0 content and incorporation of N in capping layers, and also on their porosity. We also report on the electrically active defects which are introduced in Si02 capped and annealed n-GaAs, and relate them to the intermixing process.
Degradation of Intersubband Transitions in Electron Irradiated GaAs/AlGaAs Multiple Quantum Wells With Superlattice Barriers
Authors: Morath C.P. , Manasreh M.O. , Gingrich H.S. , Bardeleben H.J. von , Ballet P. , Smathers J.B. , Salamo G.J. 
Published: April 2011

AbstractIntersubband transitions in GaAs/AIGaAs multiple quantum wells (MQWs) are studied as a function of 2 MeV electron irradiation doses using the optical absorption technique. The MQW structure was designed with a 5 period Al.4Ga.6As/GaAs superlattice barrier, and two transitions are observed in the spectra. These transitions occur from the ground state to the first excited state and to the miniband formed by the superlattice barrier. The total integrated area from both transition spectra are studied as a function of temperature and electron irradiation dose. For the ground state to first excited state transition the total integrated area decreases exponentially as the irradiation dose increases, which could be explained in terms of the trapping of the 2D-electron gas in the quantum well by the irradiation induced defects. In comparison, the intensity of the ground state to miniband transition was found to increase exponentially as a function of the irradiation dose. Two possible explanations for this behavior are suggested. The temperature dependence of the integrated area of both transitions is also presented.
Compound Semiconductor Applications for Automotive Sensors
Authors: Pelczynski M. W. , Heremans J. J. , Schwed S. 
Published: April 2011

AbstractCompound semiconductors find extensive application as magnetic position sensors in the automotive environment. Typical applications involve the sensor element, a permanent magnet attached to the sensor, and a moving magnetic circuit -a target wheel. Wider mechanical gaps in the magnetic circuit can be utilized with a sensor of higher sensitivity, and thus high sensitivity is valuable. Further limitations on the choice of materials are imposed by temperature sensitivity, as the automotive environment is characterized by wide temperature operating ranges (-40°C up to 200°C). The magnetic signal may be hidden by the temperature drift in the sensor output, andthus temperature stability limits the sensor's resolution. Automotive position sensors find use in ignition timing and misfire detection (cam and crank sensors), as wheel speed sensors (anti-lock brakes and other types of active wheel-control), in brushless electric motors and several other applications. This work reviews progress achieved to refine the use of InSb for automotive sensing applications.
Correlation Between GaInAsSb Surface Step Structure and Phase Separation
Authors: WANG C.A. 
Published: April 2011

AbstractA strong correlation between the surface step structure and phase separation in metastable GaInAsSb epitaxial layers grown by organometallic vapor phase epitaxy has been identified. The full width at half maximum (FWHM) of 4-K photoluminescence (PL) peak energy is used as a semi-quantitative measure of the degree of phase separation. The step structure of GaInAsSb grown at 525 °C is vicinal, while it is step-bunched for layers grown at 575 °C. The corresponding 4-K PL FWHM data indicate that the degree of phase separation is minimized when the layers aregrown at the lower growth temperature. It is proposed that the longer terrace lengths of a step-bunched surface are associated with a longer adatom lifetime compared to a vicinal surface, and thus the adatoms have more time to cluster and phase separate, which is the preferred equilibrium state. Increasing the growth rate, which reduces the adatom lifetime, also reduces the PL FWHM, and thus, the degree of phase separation.
Microcrystalline Si and (Si,Ge) Solar Cells
Authors: Dalal Vikram L. , Maxson Tim , Han Kay 
Published: April 2011

ABSTRACTWe report on the growth of microcrystalline Si and (Si,Ge) cells on stainless steel substrates. The devices were grown using a remote, low pressure, ECR growth technique at low temperatures (250-350 C). The precursor gases were silane, germane and hydrogen. The devices were of the p-i-n type, with light incident on the p layer. The p layer was a-(Si,C). A novel interface buffer layer, consisting of an amorphous alloy whose bandgap was graded from 1.3 eV to 1.9 eV was used to match the crystalline base layer with the higher gap p layer. It was found that the properties of this buffer layer were critical in determining the properties of the resulting device. The buffer layer was found to increase the voltage by almost 20%. Cells with high fill factors were made using this technique. The quantum efficiency data indicated that the base layers had absorption characteristic of crystalline materials.
Effects of Structural Properties of νc-Si:H Absorber Layers on Solar Cell Performance
Authors: Vetterl O. , Carius R. , Houben L. , Scholten C. , Luysberg M. , Lambertz A. , Finger F. , Wagner H. 
Published: April 2011

ABSTRACTThin film microcrystalline silicon solar cells with absorber layers of various structural composition have been prepared. The highest conversion efficiency is observed at preparation conditions close to the transition to the amorphous growth regime, i.e. crystalline volume fraction is high but not at its maximum. The optimized material consists of crystalline “fibers” with small diameter which extend through the whole absorber layer. On further approach to the transition regime a set in of amorphous growth can be observed, resulting in decreasing solar cell performance. Surprisingly, material prepared under conditions favoring highly crystalline growth exhibits a less efficient carrier extraction if applied to the solar cell. We discuss increasing bulk recombination as possible cause for this observation. The maximum conversion efficiency obtained was 8.7 % for a 1 νm single junction solar cell. Using our optimized deposition conditions with simultaneously higher discharge powers the deposition rate can be increased up to 4.6 Å/s at the high efficiency of 8.3 %.
Amorphous Silicon Alloy Solar Cells Near the Threshold of Amorphous-to-Microcrystalline Transition
Authors: Yang Jeffrey , Lord Kenneth , Guha Subhendu , Ovshinsky S.R. 
Published: April 2011

ABSTRACTA systematic study has been made of amorphous silicon (a-Si) alloy solar cells using various hydrogen dilutions during the growth of the intrinsic (i) layer. We find that the open-circuit voltage (Voc) of the cells increases as the dilution increases; it then reaches a maximum before it decreases dramatically. This sudden drop in Voc is attributed to the transition from amorphous silicon to microcrystalline inclusions in the i layer. We study i-layer thicknesses ranging from 1000 Å to 5000 Å and find that the transition occurs in all thicknesses investigated. Based on this study, a-Si alloy p i n solar cells suitable for use in the top cell of a high efficiency triple-junction structure are made. By selecting an appropriate dilution, cells with Voc greater than 1 V can be achieved readily. Solar cells made near the threshold not only exhibit higher initial characteristics but also better stability against light soaking. We have compared top cells made near the threshold with our previous best data, and found that both the initial and stable efficiencies are superior for the near-threshold cells. For an a-Si/a-Si double-junction device, a Voc value exceeding 2 V has been obtained using thin component cells. Thicker component cells give rise to an initial active-area efficiency of 11.9% for this tandem structure.
Protocrystalline Growth of Silicon below 80°C
Authors: Koch Christian , Ito Manabu , Svrcek Vlado , Schubert Markus B. , Werner Jürgen H. 
Published: April 2011

ABSTRACTProtocrystalline silicon deposited at temperatures below 80°C exhibits an extraordinary photosensitivity and superior stability against light-soaking. This material growths at the borderline of the amorphous and nanocrystalline phases in plasma-enhanced chemical vapor deposition. After thermal annealing and subsequent light-soaking, the photosensitivity is comparable to the values after deposition, while amorphous silicon strongly drops off. A structural and optical characterization reveals a small fraction of silicon crystallites embedded in an amorphous well-ordered matrix. We investigate the morphology of silicon films deposited at the edge of crystallinity by the absolute Constant Photocurrent Method and observe a phase transition from amorphous to nanocrystalline silicon. This thickness dependant morphology is of crucial importance for solar cell design. We attain protocrystalline absorber which reflect in a strongly improved fill factor compared to amorphous silicon based solar cells.
Early Research On Amorphous Silicon: Errors and Missed Opportunities
Authors: Fritzsche Hellmut 
Published: April 2011

ABSTRACTIt is instructive to reflect on the past research of an entirely new material such as hydrogenated amorphous silicon in order to analyze which impediments lay in the way of reaching our present understanding. What in retrospect appears to be clear and important evidence was often not recognized as such and, therefore, not incorporated into a coherent picture for a surprisingly long time. One reason for the inability to see and understand is one's mode of thinking, which is conditioned by training and prior experience. Other impediments to progress are some persuasive, but erroneous, views of respected members of the scientific community. A third factor that tends to slow progress is a false sense of competition which, for example, prevents research laboratories from a fruitful exchange of materials and samples. It appears that human faults run neck to neck with nature's intricacies in slowing the pace of our understanding.
Composition and Structure of SiCx:H Films Formed by Plasma Immersion ION Implantation From A Methane Plasma
Authors: Volz K. , Klatt Ch. , Ensinger W. 
Published: April 2011

ABSTRACTHydrocarbon ions are implanted into silicon by pulse biasing Si to a high voltage of -45 kV in a methane plasma. The resulting SiCx:H films are examined with respect to their composition and chemical binding by RBS, NRA and IR spectroscopy. The process may yield all C/Si ratios, up to pure C films. The H depth profile is shown to be strongly governed by the C depth profile. Silicon carbide bonding as well as C–H bonds can be proven in the implanted region.
Fast In-diffusion of Hydrogen at the Initial Stage of Hydrogen Plasma Treatment on a-Si:H Films Observed by In-situ ESR Measurements
Authors: Das Ujjwal Kr. , Yasuda Tetsuji , Yamasaki Satoshi 
Published: April 2011

ABSTRACTTime evolution of Si dangling bonds (dbs) was monitored during atomic hydrogen treatment of a-Si:H films using an in-situ electron-spin-resonance (ESR) technique. A high diffusion coefficient (>10−10 cm2s−1) of free atomic H in a-Si:H was detected at the very initial stage of H exposure. Atomic H diffuses into the bulk of the film (∼100 nm) and creates additional metastable dbs. The spatial distribution of such metastable dbs becomes deeper at lower treatment temperatures. An activated type of db creation reaction determines the distribution of these dbs.
Isotope Exchange in Hydrogenated Silicon-Oxynitride (SiON) for 1.55μm Optical Waveguide Applications
Authors: Lee Jinju , Cheng Kangguo , Lyding Joseph W. , Salemink Huub W.M. 
Published: April 2011

ABSTRACTWe report a novel way of reducing the unwanted absorption loss in silicon-oxynitride (SiON) waveguides by replacing nitrogen-hydrogen (N-H) bonds with nitrogen-deuterium (N-D) bonds in an isotope exchange process. D was introduced to SiON layers in an atmospheric D anneal after the deposition of SiON. The deuterated SiON showed a factor of 2 less absorption at 1.51 μm than before the D anneal. This is an additional loss reduction, since a typical pre-anneal in N2 reduces the loss by a factor of 10. Compared to the loss in as-deposited SiON at this wavelength, the loss after D anneal is reduced by a factor of 20. The D annealing temperature varied from 450 to 950 °C. There is a correlation between the loss reduction and the level of isotope exchange in the SiON waveguide, and also, an onset temperature for thermal activation of the isotope exchange. This mechanism is characterized carefully by secondary ion mass spectrometry (SIMS).
Transport Properties of Polycrystalline Silicon with Various Textures and Microstructures
Authors: Kamiya Toshio , Nakahata Kouichi , Suemasu Atsushi , Ro Kazuyoshi , Fortmann C.M. , Shimizu Isamu 
Published: April 2011

ABSTRACTCarrier transport property was studied in relation to microstructure for polycrystalline silicon (poly-Si) prepared from SiF4 and H2 gas mixtures at temperatures below 360°C. It was found that Hall mobility markedly increased with the increase in crystal fraction especially at crystal fractions larger than 80% and it exhibited good correlation with orientation fluctuation as well as with crystal fraction. In addition, dependence of Hall mobility on orientation fluctuation exhibited different tendency between (220) and (400) oriented poly-Si. It suggests that atomic configuration and electronic structure at grain boundaries depends on orientation structure, resulting in the different dependence of Hall mobility on orientation fluctuation. By applying hot-vapor annealing at 310°C to 1 μm-thick P-doped (400) oriented poly-Si, Hall mobility was improved from 10 cm2/Vs to 17 cm2/Vs.
A Laplace Transform Technique for Direct Determination of Density of Electronic States in Disordered Semiconductors from Transient Photocurrent Data
Authors: Gueorguieva Mariana J. , Main Charles , Reynolds Steve 
Published: April 2011

ABSTRACTA new technique for direct determination of the density of electronic states (DOS) in disordered semiconductors is described. It involves Laplace transformation of transient photocurrent data I(t) followed by the numerical solution of the system of linear algebraic equations obtained from the Fredholm integral of the first kind, for a DOS represented by a series of discrete levels. No approximations are used in the solution, and no prior assumptions as to the form of the DOS are made. The fidelity of this method is assessed and compared with existing techniques by application to computer-simulated I(t) data generated from single-level and continuous DOS profiles, and to experimental data.
Hydrogenated Amorphous Silicon and Silicon Nitride Deposited at less than 100° C by ECR-PECVD for Thin Film Transistors
Authors: Flewitt Andrew J. , Dyson Andrew P. , Robertson John , Milne William I. 
Published: April 2011

ABSTRACTA systematic study has been made of the growth of both hydrogenated amorphous silicon (a-Si:H) and silicon nitride (a-SiN) by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). In the case of a-SiN, helium and nitrogen gas is injected into the system such that it passes through the resonance zone. These highly ionised gases provide sufficient energy to ionise the silane gas, which is injected further downstream. It is demonstrated that a gas phase reaction occurs between the silane and nitrogen species. It is control of the ratio of silane to nitrogen in the plasma which is critical for the production of stoichiometric a-SiN. Material has been produced at 80 °C with a Si:N ratio of 1:1.3 a breakdown strength of ∼6 MV cm−1 and resistivity of >1014 Ωcm. In the case of a-Si:H, helium and hydrogen gas is injected into the ECR zone and silane is injected downstream. It is shown that control of the gas phase reactions is critical in this process also. a-Si:H has been deposited at 80 °C with a dark conductivity of 10−11 Ω−1 cm−1 and a photosensitivity of just below 4×104. Such materials are suitable for use in thin film transistors on plastic substrates.
Preparation of Microcrystalline Silicon Based Solar Cells at High i-layer Deposition Rates Using a Gas Jet Technique
Authors: Jones S.J. , Crucet R. , Deng X. , Williamson D.L. , Izu M. 
Published: April 2011

ABSTRACTA Gas Jet technique has been used to prepare microcrystalline silicon (μc-Si) thin films at deposition rates as high as 20 Å/s. The films have microcrystal sizes between 80 and 120 Å with a heterogeneous microstructure containing regions with columnar growth and other regions with a more randomly oriented microstructure. These materials have been used as i-layers for nip single-junction solar cells. The high deposition rates allow for fabrication of the required thicker μc-Si i-layers in a similar amount of time to those used for high quality a-SiGe:H i-layers (rates of 1-3 Å/s). Using a 610nm cutoff filter which only allows red light to strike the device, pre-light soaked short circuit currents of 8-10 mA/cm2 and 2.7% red-light efficiencies have been obtained while AM1.5 white light efficiencies are above 7%. These efficiencies are higher than those typically obtained for μc-Si cells prepared at the high i-layer growth rates using other deposition techniques. After 1000 h. of light soaking, the efficiencies on average degrade only by 2-5% (stabilized efficiencies of 2.6%) consistent with the expected high stability with the microcrystalline materials. The small amount of degradation compares with the 15-17% degradation in efficiencies for a-SiGe:H cells subjected to similar irradiation treatments (final light-soaked red light efficiencies of 3.2%). Improvements in the cell efficiencies may come through an understanding of the role that columnar microstructure and void structure plays in determining the device performance.
Thickness and Interface Layer Effects on the Amorphous Silicon Film Property Studied by Various Photoluminescence Excitation Wavelengths
Authors: Yue Guozhen , Han Daxing , Yang Jeffrey , Guha Subhendu 
Published: April 2011

ABSTRACTWe have studied the structure of highly hydrogen-diluted a-Si:H films by using Raman and photoluminescence (PL) spectroscopies. Raman spectra show a typical broad a-Si:H peak in the films with different substrate surfaces or i-layer thicknesses, except for one 1.4 μm film deposited directly onto a stainless steel (ss) substrate that shows the c-Si peak. An apparent μc-Si component was characterized by a low energy PL enhancement in a 0.5 μm film deposited directly onto the ss substrate. When a thin n-layer was inserted between the substrate and the a-Si film, no μc-Si growth was found in the first 0.5-1.0 μm thick layer but there was a μc-Si component in the top surface layer when the film was grown to a 1.5 μm thickness. The nonuniformity structure along the growth direction was characterized by PL spectroscopy using varied laser excitation wavelengths of 325, 488, 514.5, and 632.8 nm. We find that PL spectroscopy is a sensitive tool to characterize the microcrystallinity of the film.
In-line Characterization of Thin Polysilicon Films by Variable Angle Spectroscopic Ellipsometry
Authors: Paprotta S. , Röver K. S. , Ferretti R. , Höhne U. , Kähler J. D. , Haase J. 
Published: April 2011

ABSTRACTUp to now an in-line method for parameter determination of deposited thin polysilicon films is not available. In this paper a method for monitoring the polysilicon deposition process in device manufacturing by variable angle spectroscopic ellipsometry (VASE) is demonstrated. Therefore several polysilicon films are deposited on thermally oxidized [100] silicon wafers. These samples are characterized by VASE in the optical range of 450 - 850 nm. Parameters are determined by simulation using a multilayer model consisting of air, interface layer (surface roughness), polysilicon, SiO2 and silicon substrate. Different optical models representing the properties of polysilicon are tested. The free parameters are the oxide thickness, the composition and the thickness of the interface layer (air, polysilicon) as well as the thickness and the complex refractive index of the polysilicon layer. Results of the spectroscopic analysis are verified by AFM and SEM measurements. It can be shown that parameters of the deposited polysilicon films, which often could only be determined by complex and destructive off-line analysis methods are also accessible by non-destructive in-line VASE measurements.
Electromigration Reliability of Dual-Damascene Cu/Oxide Interconnects
Authors: Ogawa Ennis T. , Blaschke Volker A. , Bierwag Alex , Lee Ki-Don , Matsuhashi Hideki , Griffiths David , Ramamurthi Anup , Justison Patrick R. , Havemann Robert H. , Ho Paul S. 
Published: April 2011

AbstractAn electromigration study has determined the lifetime characteristics and failure mode of dual-damascene Cu/oxide interconnects at temperatures ranging between 200 and 325 °C at a current density of 1.0 MA/cm2. A novel test structure design is used which incorporates a repeated chain of “Blech-type” line elements. The large interconnect ensemble permits a statistical approach to addressing interconnect reliability issues using typical failure analysis tools such as focused ion beam imaging. The larger sample size of the test structure thus enables efficient identification of “early failure” or extrinsic modes of interconnect failure associated with process development. The analysis so far indicates that two major damage modes are observable: (1) via-voiding and (2) voiding within the damascene trench.