bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spin-Dependent Recombination Effects in a-SI:H Pin Solar Cell Devices: A New Characterization Technique
Authors: Lips Klaus 
Published: April 2011

ABSTRACTElectrically detected magnetic resonance (EDMR) - also often referred to as spin-dependent photoconductivity - is a particularly attractive technique for the investigation of the electronic properties of semiconductor devices. This method detects the paramagnetic states involved in transport and recombination by recording changes of the sample current induced by a resonant enhancement of the recombination rates. This is in contrast to ESR which monitors the resonant enhancement of microwave absorption. Therefore, EDMR is more sensitive by many orders of magnitude than conventional ESR and can be used to investigate a-Si:H solar cell devices under standard operating conditions.In this report we review the EDMR technique and discuss, in detail, the spin-dependent processes controlling dark and photocurrent of standard a-Si:H pin solar cells. In particular, we show that EDMR is sensitive to changes in the internal field of the i layer. We compare the experimental results to numerical calculations of the potential profiles and of EDMR-related quantities. We arrive at the conclusion that degradation by both high forward current and illumination increases the defect density mainly in the i layer, rather than at the pi interface.
μτ Products of 10−6 cm2V−1 Deduced from Eleverse-Bias Dependence of Carrier-Collection Measurements in High Drift Mobility a-Si:H
Authors: Ganguly Gautam , Matsuda Akihisa 
Published: April 2011

ABSTRACTThe room temperature hole drift mobility measured by the ‘time-of-flight’ technique can be increased to 0.5 cm2/Vs with a valence band tail width of 25meV by optimizing the ion impingement energy during film growth using a triode configured PECVD reactor. The reverse bias dependence of the carrier collection in Au Schottky diodes formed on these specimens show significantly improved carrier collection which can be approximately quantified using the C-V measured voltage dependent depletion widths to yield μτ≈10−6cm2V−1.
Influence of Precursor Chemistry on Synthesis of Silicon-Carbon-Germanium Alloys
Authors: Todd Michael , Kouvetakis John , Matsunaga Phillip , Chandrasekhar D. , Smith David 
Published: April 2011

ABSTRACTWe describe the synthesis and use of the novel molecular precursors C (SiH3) 4, CH3GeH3and SiH3GeH3 to generate silicon-carbon-germanium materials by ultrahigh vacuum chemical vapor deposition. By using these precursors in reactions with S1H4 and GeH4 between 470°C and 650°C we obtained: 1) heteroepitaxial Si1-x-y. GexCy (y=0.04–0.06) alloys with C (SiH3) 4; (2) polycrystalline alloys with carbon compositions ranging from 2–14 at.% with CH3GeH3; (3) mixtures of diamond cubic nanocrystals (Ge, Si1-xGex) and amorphous SiC with SiH3CH2GeH3. The effect of the precursor chemistry on composition, crystallinity, and microstructure of the materials as characterized by Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) is discussed.
Amorphous-to-Microcrystalline Silicon Transition in Hot-Wire Chemical Vapor Deposition
Authors: Brogueira P. , Chu V. , Conde J. P. 
Published: April 2011

ABSTRACTThe conductivity and the structural properties of thin films deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) from silane and hydrogen at a substrate temperature of 220 °C are shown to be strongly dependent on the filament temperature, Tfil, and process pressure, p. Amorphous silicon films are obtained at low pressures, p < 3 × 10−2Torr, for Tfil ∼ 1900 °C and FH2 = FSiH4. At this TfilJU, high deposition rates are observed, both with and without hydrogen dilution, and no silicon was deposited on the filaments. At Tfil ∼ 1500 °C, a transition from a-Si:H for p > 0.3 Torr to microcrystalline silicon (μc-Si:H) for p < 0.1 Torr occurs. In this temperature regime, silicon growth on the filaments is observed. /ic-Si:H growth both without hydrogen dilution and also in very thin films (∼ 0.05 μm) is achieved. Raman and X-Ray spectra give typical grain sizes of 10 – 20 nm, with a crystalline fraction higher than 50%. For both, Tju ∼ 1500 °C, p > 0.3 Torr and Tfil ∼ 1900 °C and p ∼ 2.7 × 10−2Torr, an increase of the crystalline fraction from 0 to ∼ 30% is observed when the hydrogen dilution, FH2/FSiH4, increases from 1 to > 4.
Real Time Monitoring of Amorphous Silicon Solar Cell Fabrication
Authors: Lu Yiwei , Kim Sangbo , Burnham J. S. , Chen Ing-Shin , Lee Yeeheng , Strausser Y. E. , Wronski C. R. , Collins R. W. 
Published: April 2011

ABSTRACTWe have applied real time spectroscopie ellipsometry (RTSE) to monitor the successive growth of p-type a-Si1-xCx:H and i-type a-Si:H on specular SnO2:F (i.e., the superstrate solar cell configuration) in a single-chamber deposition system. Both the microstructural evolution, which includes the surface roughness and bulk layer thicknesses versus time and bulk layer void volume fraction, as well as the optical properties, which include the dielectric function (1.5–4.0 eV) and optical gap of the individual layers, were determined from RTSE data collected during growth. The accuracy of our approach is demonstrated by correlating structural parameters obtained both by RTSE and atomic force microscopy. Based on prior information deduced by RTSE, the TCO/p/i structure was fabricated with optimized procedures that have sought to minimize TCO/'p and p/i interfacial problems. These studies illustrate that RTSE can be a valuable tool for identifying problems in the fabrication of a-Si:H solar cells and ultimately improving cell performance.
Low Temperature Deposition of Polycrystalline Silicon thin Films by Hot-Wire CVD
Authors: Yu Shuangying , Deshpande Sadanand , Gulari Erdogan , Kanicki Jerzy 
Published: April 2011

ABSTRACTIn this study, we have deposited polycrystalline silicon (poly-Si) thin films by hot-wire Chemical Vapor Deposition (CVD) using hydrogen and disilane as the reactive gases. We selectively activate hydrogen and let disilane bypass the hot tungsten filament assembly and enter the reactor downstream from hydrogen. This may provide a better process chemistry, and by this approach, we have deposited poly-Si films at a substrate temperature as low as 310°C and at a growth rate as high as 100 Å/min. The substrate temperature is more than 2000C lower and the growth rate is more than twice higher compared to those of LPCVD poly-Si films. The effect of hydrogen flow rate, disilane flow rate and substrate temperature on the deposition rate and structural properties of the polysilicon films are investigated. The deposited films are characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and X-ray diffraction.
Dielectric Effects in Laser-Crystallised Polycrystalline Silicon Thin Film Transistors
Authors: Masterton G. H. , Gibson R. A. G. , Hack M. 
Published: April 2011

ABSTRACTWe present experimental results on the transient response of the source-drain current of laser crystallised polycrystalline silicon (poly-Si) thin film transistors (TFTs) over many orders of magnitude in time after the application of a voltage pulse to the gate electrode. This work follows on from similar measurements performed on amorphous silicon (a-Si) TFTs. Results showed a definite change in transient behaviour dependent on the magnitude of the gate bias. At a gate voltage of 5V there was an initial decay then a marked increase in the source-drain current beyond 1000 seconds. This variation of transient behaviour with gate bias was not seen in the a-Si case. For poly-Si the transient behaviour could not be split into different regimes in time (beyond the carrier transit time) whereas for a-Si TFTs the source-drain current showed a logarithmic decay at room temperature up to 100 seconds followed by a power law decay beyond 100 seconds. Our results indicate perhaps that only one mechanism exists for the observed transient decay of current, unlike the a-Si case. Measurements carried out at elevated temperature showed the current decay was independent of temperature indicating that the transient decay may be caused by charge injection via a tunnelling process into interface states, gate dielectric or passivation dielectric. Finally by carrying out measurements on TFTs after moderate positive voltage stressing and on TFTs with specially fabricated gate and passivation dielectrics it has been established that the transient decay is dielectric related and not a defect generation process.
TFT Performance - Material Quality Correlation for a-Si:H Deposited at high Rates
Authors: Sherman S. , Lu P-Y. , Gottscho R. A. , Wagner S. 
Published: April 2011

ABSTRACTWe evaluated the characteristics of a-Si:H/a-SiNx:H thin film transistors (TFTs), and of separately deposited a-Si:H films, as functions of the a-Si:H deposition power in a high-rate, large-area, 40 MHz PE-CVD system. TFT performance and a-Si:H film properties improve with decreasing power density and deposition rate. However, low defect density a-Si:H material was deposited at rates as high as 1500 Å/min. TFTs with gate nitride deposited at 1000 A/min show excellent I-V characteristics when the a-Si:H deposition power is low enough. The TFT electron mobility in the linear regime correlates well with the Urbach energy of the a-Si:H films, suggesting that the quality of the a-Si: H controls the performance of our TFTs.
Two Dimensional Amorphous Silicon Image Sensor Arrays
Authors: Street R. A. , Wu X. D. , Weisfield R. , Ready S. , Apte R. , Nguyen M. , Nylen P. 
Published: April 2011

ABSTRACTLarge two dimensional amorphous silicon image sensor arrays offer a new approach to electronic document input and x-ray imaging. The sensor array technology is now capable of image capture at greater than 10 frames/sec and with resolution of 200–400 spi. We describe our new high resolution imaging system, comprising a page-sized sensor array with nearly 3 million pixels, and the accompanying high speed read out and processing electronics. The key technological issues of pixel resolution, sensor fill factor, leakage currents and noise are reviewed. Measurements of a new array architecture are described, in which the sensor is formed as a single continuous film on top of the matrix addressing components.
Thick Amorphous Silicon Layers Suitable for the Realization of Radiation Detectors
Authors: Hong W. S. , Petrova-Koch V. , Drewery J. , Jing T. , Lee H. , Perez-Mendez V. 
Published: April 2011

ABSTRACTThick silicon films with good electronic quality have been prepared by glow discharge of He-diluted SiH4 at a substrate temperature ∼150°C and subsequent annealing at 160°C for about 100 hours. The stress in the films obtained this way decreased to ∼100 MPa compared to the 350 MPa in conventional a-Si:H. The post-annealing helped to reduce the ionized dangling bond density from 2.5 × 1015 cm−3 to 7 × 1014 cm−3 without changing the internal stress. IR spectroscopy and hydrogen effusion measurements implied the existence of microvoids and tiny crystallites in the material showing satisfactory electronic properties. P-I-N diodes for radiation detection applications have been realized out of the new material.
Adjustable Threshold a-Si/SiC:H Color Detectors
Authors: de Cesare Giampiero , Irrera Fernanda , Lemmi Francesco , Palmamario Tucci Fabrizio 
Published: April 2011

ABSTRACTWe present the Adjustable Threshold Color Detectors (ATCDs) based on stacked heterojunctions of amorphous silicon (a-Si:H) and silicon carbide (a-SiC:H). These devices work as bias-controlled photocurrent sources with different values of the voltage threshold depending on the wavelength of the incident radiation. The ATCDs detect the three fundamental chromatic components (blue, green, red) by varying the external voltage within a few Volts.
Surface Passivation and the Ultrafast Optical Response of Low-Temperature-Grown GaAs
Authors: Wang H. H. , Whitaker J. F. , Al-Hemyari K. , Williamson S. L. 
Published: April 2011

AbstractMetal-semiconductor-metal photodetectors fabricated using low-temperature-grown GaAs have been passivated using AlGaAs cap layers in order to understand the influence of surface states and fields on the properties of these detectors. It has been found that passivation has little effect on the time response or persistent photoconductive tails associated with the detectors, but that responsivity and dark current can be enhanced in certain circumstances. The dependence of the temporal response on optical fluence and dc-voltage bias were observed for both passivated and unpassivated detectors.
Incorporation of Hydrogen in SiO2 and Si3N4 Thin Films Deposited by ECR-CVD
Authors: Brown J. , Boudreau M. , Boumerzoug M. , Mascher P. , Jackman T. E. , Tong S. Y. , Haugen H. 
Published: April 2011

AbstractHydrogen incorporation in ECR-CVD silicon oxynitride films deposited using tris dimemylaminosilane (TDAS) as the silicon precursor was investigated. The as-deposited silicon dioxide films were shown to contain little hydrogen (<2%) as determined by both FTTR and nuclear reaction analysis (15N profiling). Films were obtained with high breakdown fields (>10 MV/cm) and low interface state densities (2×l011cm−2) on silicon without special surface preparation. Silicon nitride films were found to contain large hydrogen concentrations, both bonded and unbonded, which evolved from the film due to beam irradiation during 15N profiling. We were able to demonstrate that dilution of the nitrogen plasma with both hydrogen and argon was effective in avoiding problems of trace oxygen contamination and poor film adhesion, and reducing the hydrogen concentration in the nitride films.
Atomic Structure of Deep Level Defects in Dimethylaluminum Methoxide-Doped GaAs
Authors: Park Y , Skowronski M 
Published: April 2011

AbstractGaAs epilayers doped with dimethylaluminum methoxide (DMA1MO), an alkoxide bearing a pre-formed Al-O molecule, have been investigated using local vibrational mode (LVM) absorption and deep level transient spectroscopy measurements. LVM measurements indicated that oxygen and aluminum atoms are incorporated into GaAs layer as a complex and remain bound in the volume of the crystal. Electron traps with activation energies of 0.74 and 0.93 eV below the conduction band are main deep level defects responsible for the electrical and optical properties of the layers. Interpretation of the relationship between trap concentration and growth conditions led to the conclusion that the 0.93 and 0.74 eV traps have the atomic structures in which oxygen atom is bonded to one (AlO) and two aluminum atoms (A12O), respectively.
Very Low Deep Level AlxGa1−xAs (x=0.22) Layer Grown by Metalorganic Chemical Vapor Deposition
Authors: Huang Z. C. , Yang Bing , Chen H. K. , Chen J. C. 
Published: April 2011

ABSTRACTWe have achieved deep-level-free Al0.22Ga0.78As epitaxial layers using low selenium (Se)-doping (8.4 × l016 cm−3) grown by metalorganic chemical vapor deposition (MOCVD). Deep levels in various Al0.22Ga0.78As layers grown on GaAs substrates were measured by deep level transient spectroscopy (DLTS). We have found that the commonly observed oxygen contamination-related deep levels at EC-0.53 and 0.70 eV and germanium-related level at EC-0.30 eV in MOCVD-grown Al0.22Ga0.78 As can be eliminated by low Se-doping. In addition, a deep hole level located at Ev+0.65 eV was found for the first time in highly Se-doped Al0.22Ga0.78 As epilayers. We suggest that low Se-doping (<2 × 1017 cm−3) produces a passivation effect and then deactivates other deep levels in Al0.22Ga0.78As.
Spectroscopic Ellipsometric Characterization of Low Temperature GaAs
Authors: Gao X. , Snyder P. G. , Yu P. W. , Zhang Y. Q. , Peng Z. F. 
Published: April 2011

AbstractPseudodielectric functions of low temperature grown GaAs (LT GaAs) measured by spectroscopic ellipsometry are presented. The spectral range includes the El (2.92eV) and El+ΔAl (3.13eV) critical point structure of GaAs. A Lorentz-oscillator model was used to fit the dielectric function of LT GaAs for samples with nominal growth temperatures (Tg) varying from 200°C to 580°C. For Tg of 200°C, 30% and 19% broadenings and −0.01 leV and −0.007eV red shifts were found for the El and El+Δl structures respectively, compared with normal GaAs. The red shift can be explained in terms of a strain effect in the LT layer. In annealed LT GaAs the broadening decreased significantly and no red shift was found.
Transition-Metal Impurity Luminescence in GaAs and its Application to Material Characterization
Authors: Nishino T. 
Published: April 2011

AbstractA number of sharp characteristic luminescence lines has been observed for GaAs doped with 3d transition-metal impurities in the near-infrared region, the origin being attributed to the zero-phonon intracenter transitions between the energy levels of the metal ions split by the crystal field of the GaAs lattice. It is also known that these luminescence lines are very sensitive to the surrounding field of the transition-metal impurities. The luminescence of Cr-doped GaAs has been most extensively studied, the spectrum revealing a very sharp luminescence line at 0.839 eV. In this paper we review the results on the successful applications of this Cr-related luminescence line to characterization of in-depth profiles of arsenic vacancy in thermally annealed GaAs, local strain field in In-doped GaAs and interface stress at heterostructures grown on Cr-doped GaAs substrate.
Coupling of Electronic and Structural Properties of Hydrogen in Crystalline Silicon
Authors: Csaszar Wolfgang , Endrös Arthur L. 
Published: April 2011

AbstractTheory has made great progress during recent years in calculating the fundamental properties of monatomic hydrogen in crystalline silicon. By applying the DLTS and DDLTS method we use the hydrogen-carbon complex which consists of an electronically inactive carbon atom on a substitutional lattice site and a hydrogen atom near the bond-center position to detect theoretically predicted properties of hydrogen in silicon. The results of two independent experiments show that there exists a coupling of the electronic and structural properties of monatomic hydrogen, as predicted by theory.
Interaction of Atomic Hydrogen with Chalcogens in Gaas
Authors: Vetterhöffer J. , Weber J. 
Published: April 2011

AbstractThe passivation by hydrogen of the shallow donors sulfur, selenium, and tellurium in GaAs was studied by infrared absorption spectroscopy (FTIR), capacitance-voltage (CV) depth profiling, and secondary ion mass spectroscopy (SIMS). Local vibrational mode (LVM) frequencies due to hydrogen-donor complexes agree with a microscopic model where the hydrogen atom is bound in the antibonding position to one of the donor’s neighboring gallium atoms. Our results suggest a hydrogen penetration depth much greater than the passivated region, however the infrared active region coincides with the passivated part of the material.
Plasma-Induced Electron Traps in n-InP
Authors: Sakamoto Yoshifumi , Sugino Takashi , Matsuda Koichiro , Shirafuji Junji 
Published: April 2011

AbstractDeep electron traps in n-InP introduced during plasma exposure have been studied by means of isothermal capacitance transient spectroscopy (ICTS). Three electron traps, (Ec–0.21 eV), (Ec–0.34 eV) and (Ec–0.54 eV), which are designated E2, E3 and E4, respectively, are detected in n-InP treated with H2 plasma and by subsequent annealing. The E2 trap is induced by plasma exposure and the E3 trap is produced by thermal annealing. The E4 trap is generated by both plasma exposure and thermal annealing. These three traps are passivated with hydrogen atoms. The E2 trap density near the surface of hydrogen-plasma-treated samples is strongly enhanced by applying electric field because of dissociation of hydrogen from E2 trap. The E2 trap is annealed out with the activation energy of 1.5 eV and the attempt-to-escape frequency of 3.2 × 1014 s−1. Phosphine plasma treatment is effective in suppressing generation of these electron traps.
Hydrogen Diffusion and Passivation in InGaAIN Alloys
Authors: Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Vartuli C. B. , Wilson R. G. , Zavada J. M. , Shul R. J. 
Published: April 2011

AbstractHydrogen is found to readily diffuse into InGaN, InAIN and InGaAIN epitaxial layers during plasma exposures at 170 – 250 °C for 40 sec - 30 min. The diffusivity of hydrogen is > 10−11 cm2-s−1 at 170 °C, and the native donor species are passivated by association with the hydrogen. Reactivation of these species occurs at 450–500°C, but the hydrogen remains in the material until ≥ 800 °C.
Photoconductivity as a Function of Temperature in MOCVD Grown Gallium Nitride Films
Authors: Qiu C. H. , Melton W. , Pankove J. I. 
Published: April 2011

AbstractThe optical absorption in gallium nitride (GaN) films was studied by photoconductivity (PC) spectroscopy at various temperatures. At all the measured temperatures, the photoconductivity per incident photon increases with photon energy hv from 1.8 eV to 3.0 eV approximately as exp(hv/E0). Surprisingly, the measured photoconductivity tail to the infrared becomes more pronounced in magnitude at lower temperatures. We suggest from the data that the photoconductivity is dominated by majority carriers, and that the quantum efficiency η for conducting electron and hole generation by across-gap excitation increases with increasing temperature.
Surface-Oriented Oxygen Mass Transport During Implantation
Authors: Danilin A. B. , Charnyi L. A. , Nemirovski A. W. , Saraikin V. V. 
Published: April 2011

AbstractThe effect of implantation conditions on the localization of oxygen implanted with substoichiometric doses has been studied. Oxygen ions were implanted into Si wafers coated with a thin oxide film, which was etched off after the implantation. We used various implantation modes. After the implantation, the specimens were studied using SIMS and X-ray diffractometry. The concentration profiles suggest that at the lower implantation temperature, part of oxygen migrates toward the Si-SiO2 interface. The effect does not refer to the usual enhancement of SIMS signal at the surface because the concentration peak is at a depth of about 25 nm. Calculated deformation profiles indicate a compression at the same depth, the effect being the strongest for the low current density. The result suggests that the superficial layer is rich in vacancial-type defects. The coincidence of the deformation and oxygen concentration maxima leads to the conclusion that oxygen migrates toward the surface in the form of A-centers. A similar phenomenon has been observed for sequential low-temperature implantation of oxygen and nitrogen.
Observation of Vacancy-Oxygen Complexes in Silicon Implanted with Substoichiometric Doses of Oxygen Ions
Authors: Belogorokhov A. I. , Charnyi L. A. , Danilin A. B. , Nemirovski A. W. 
Published: April 2011

AbstractCz-grown p-Si(111) specimens were implanted with O+ ions at an energy of 150 keV and doses of 0.25, 0.5, and 1.0 (·1017) cm−2. The implantation temperatures used were 350 and 650 °C. After the implantation, some of the specimens were annealed at 1000 °C for 1 h in a nitrogen atmosphere. IR data indicated the presence of vacancy-oxygen complexes both before and after annealing, irrespective of implantation temperature. Double-crystal X-ray rocking curves also showed that vacancy-type defects are present.