bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non-Gaussian 1 / f Noise and Conductance Fluctuations in Hydrogenated Amorphous Silicon
Authors: Parman C. E. , Israeloff N. E. , Kakalios J. 
Published: March 2011

ABSTRACTStatistical analysis of the 1/f noise power spectrum of co-planar current fluctuations in n-type doped hydrogenated amorphous silicon (a-Si:H) find that the noise arises from a small number of correlated fluctuators. The noise power displays a complicated time dependence with the noise power changing in both magnitude and as a function of frequency. Spectral analysis of these noise power fluctuations display an approximate 1/f frequency dependence. These results are surprising given the effective volume (∼10-7 cm3) of the sample, and indicate that cooperative dynamics govern conductance fluctuations in a-Si:H.
Quasi-Fermi Energy and Steady-State Recombination Demarcation Level in a-Si:H
Authors: Liu J. Z. 
Published: March 2011

ABSTRACTA specially designed photoconductivity experiment directly shows that, above room temperature, the steady-state recombination lifetime of the free electrons in undoped amorphous silicon can be described by the free electron quasi-Fermi energy alone. The apparent discrepancy on recombination demarcation levels between the Rose model and the Simmons-Taylor model is resolved by including the effect of the occupation function. The significance of the free electron quasi-Fermi level is discussed.
Mobility-Lifetime Products in a-Si:H and the Dangling Bond Recombination Model
Authors: Morgado E. 
Published: March 2011

ABSTRACTFermi level and light intensity dependences of electron and hole lifetimes have been calculated using a recombination model which considers positively correlated dangling bonds as the only localized states in the gap. The model equations have been solved numerically taking into account the non-equilibrium statistics of correlated electrons and the Fermi level dependence of the defect density. The results are in agreement with the anticorrelated behavior of the majority' and minority carrier μτ products observed in a-Si:H. The majority carrier lifetime is found to be more sensitive to the photogeneration rate than the minority carrier lifetime. The position of the Fermi level with respect to the energies of the D° and D- centers in the gap is a determinant factor of the (°τ)e/(μτ)h ratio.
Assessment of Free Electron to Free Hole Ratios in a-Si:H By Ambipolar Diffusion and Photoconductivity Measurements
Authors: Pipoz Patrice , Sauvain Evelyne , Hubin Jacques , Shah Arvind 
Published: March 2011

ABSTRACTThe authors report on systematic photoconductivity σph and ambipolar diffusion length Lamb measurements carried out on a series of lightly p- and n-doped samples and monitored throughout the entire light-induced degradation process. The results are interpreted based on a transport model involving free carriers (nf and pf), localized charge on bandtails, as well as dangling bond and dopant charges.
Loss Peaks in the AC Conductivity of a-Si:H
Authors: Schirone L. , Guseinov Ya. Yu. , De Cesare G. , Ferrari A. , Califano F.P. 
Published: March 2011

ABSTRACTThe electrical conductivity of a-Si:H films was investigated in the temperature range 300K - 450K under an alternative electric field whose frequency was in the range 100 Hz - 6×106 Hz. Loss peaks were detected, located at a temperature dependent frequency and superimposed to a nearly linear dependence on frequency. Their amplitude has found to be sensitive to Staebler-Wronski Effect. The observed photodegradation-sensitive loss peaks have been described in terms of a Simple Pair Hopping (SPH) mechanism, involving the electronic states associated to dangling bonds, superimposed to a broadband process described by Correlated Barrier Hopping (CBH) model.
Toward 20% Efficiency With a-Si // poly-Si Tandem Solar Cell
Authors: Yoshimi M. , Ma W. , Horiuchi T. , Lim C. C. , De S. C. , Hattori K. , Okamoto H. , Hamakawa Y. 
Published: March 2011

ABSTRACTA series of experimental investigations has been made on the a-Si // poly-Si tandem solar cell which is one of the most promised candidate of high cost-performance photovoltaic cell, e.g., high efficiency, low cost with almost no light induced degradation. Employing high conductivity with wide optical band gap p type microcrystalline SiC (μ-SiC) as a window material together with a-SiC as an interface buffer layer and also n type μc-Si as a back ohmic contact layer in the poly-Si based bottom cell, the conversion efficiency of 17.2 % has been obtained. Combining an optically transparent a-Si p-i-n cell as a top cell with an optical coupler between the top and the poly-Si bottom cell, a total efficiency of 20.3 % has been obtained so far on the four-terminal stacked mode structure. A systematic technical data for the optimization of cell structure variation on the developed tandem solar cells are presented and further possibility to improving the performance are discussed.
Hydrogenation of B and P Implanted LPCVD Amorphous Silicon
Authors: Pietruszko Stanislaw M. 
Published: March 2011

ABSTRACTThe results of the investigation of doping by B and P ion implantation into LPCVD amorphous silicon films in the range from 2*1015 to 2*1021 atoms/cm3 are presented. The room temperature conductivity increases to 10-2 Ω-1 cm-1 and to 10-2 Ω-1 cm-1 for the highest B and P doping, respectively. The subsequent hydrogenation (2.5 and 5 at%) by ion implantation increases the doping efficiency for P doping. For B doping efficiency increases at the low and decreases for the high doping range. The results of conductivity measurements vs temperature of doped and hydrogenated films are presented.
High Quality a-SiO:H Films and Their Application to a-Si Solar Cells
Authors: Fujikake S. , Ohta H. , Asano A. , Ichikawa Y. , Sakai H. 
Published: March 2011

ABSTRACTHydrogenated amorphous silicon oxide (a-SiO:H) films were prepared by rf glow discharge decomposition of SiH4, CO2 and H2 gas mixture. These films showed better properties than a-SiC:H films. By applying the a-SiO:H to the p-layer, we attained an efficiency of 12.5% for 1cm2 single junction solar cells and a total-area efficiency of 10.1% for 30cm × 40cm tandem submodules.
Effects of Low Level Graded I-Layer Doping on the Stability of A-SI:H Solar Cells
Authors: Fischer D. , Pellaton N. , Keppner H. , Shah A. , Fortmann C. M. 
Published: March 2011

ABSTRACTThis work reports on attempts to tailor the electric field of a-Si:H solar cells by the graded low-level doping of the intrinsic layer to optimize conversion efficiency in the degraded state. Based on wavelength dependent collection measurements and numerical modeling, the degradation behavior of doped and undoped cells is explained in terms of the interaction of dopants and the light-induced space-charge. Low level doping is shown to shift the electric field away from the p/i interface towards the bulk of the i-layer. This results in a better carrier collection from the back part of the solar cell, and solar cells with improved stabilized red light conversion efficiency can be realized. These cells can be readily applied as bottom cells of stacked solar cells.
Effect of Plasma Treatment of the Tco on a-Si Solar Cell Performance
Authors: Demichelis F. , Galloni R. , Madan A. , Pirri C.F. , Rava P. , Ruth M. , Schropp R.E.I. , Summonte C. , Tresso E. 
Published: March 2011

ABSTRACTSingle junction a-Si p-i-n solar cells have been deposited by an Ultra High Vacuum (UHV) Multichamber PECVD system reaching an efficiency of 10.1% over 0.1 cm2 and 9.7% over 1 cm2. The effect of hydrogen treatments on the performance of the solar cells was studied on two different types of SnO2 coated substrates and was correlated with the I-V characteristics under AM1.5 (100 mW cm-2) illumination and the spectral response of the devices. The results show that modifications at the TCO/p-layer interface due to the hydrogen plasma treatments are strongly dependent on the initial characteristics of the TCO.
Characterization of the SnO2/a-SiC:H Interface in Amorphous Silicon Solar Cell by C-f-T Measurements
Authors: Caputo D. , De Cesare G. , Irrera F. , Palma F. , Salvatori S. , Vincenzoni R. 
Published: March 2011

ABSTRACTIn this paper we present a new method for the characterization of the interface between the transparent conductive oxide (TCO) and the p doped amorphous silicon carbide layer in solar cells. The method is based on electrical capacitance measurements versus frequency in the temperature range: 20K-200K. We use Schottky diode structures (TCO-p-i-Ag) containing the p-i structure actually present in solar cells. Analysis of capacitance at different frequencies allows one to calculate an“activation energy”. Activation energy, temperature, position and shape of the capacitance step can be related to the density of states in the p type material by a model here presented. The effects of the p layer thickness and of the carbon content are investigated. A large increase of activation energy at short thickness is found, which can be related to interface damage, increasing in material with high carbon content. The technique shows an high spatial resolution and has the advantage to investigate the material as grown in the actual device.
Film Morphology, Excess Shunt Current and Stability in Triple-Junction Cells
Authors: McMahon T.J. , Bennett M.S. 
Published: March 2011

ABSTRACTWhen a textured conductive textured oxide (CTO)-glass substrate is used for either thin single p-i-n or thin multilayer p-i-n structures, a new mode of light-induced cell degradation occurs which has been associated with enhanced shunting. In this study, triple-junction cells were examined before and after light-soaking using dark current-voltage (I-V) analysis. Two degradation mechanisms are occurring: i) The classical bulk Staebler-Wronski defect generation mechanism causes an increase in diode quality factor, ii) In cells exhibiting more as-grown shunting behavior, light-soaking greatly enhances shunting. This enhanced shunting becomes the primary mode of degradation.Reversible incremental current steps are also seen when measuring the (I-V) characteristics on diodes with excess shunt current due to light-soaking. This is a clear indication that the increase in shunting is caused by an increase in the number of shunt pathways and not by enhancing current through existing shunts. Optical-beam-induced current (OBIC) scans show some small defect areas of reduced current responsivity that are about 5–10 urn in diameter and may not be caused by holes in the back reflector metalization. Localized accelerated light-induced degradation is measured using the OBIC scanning laser beam on small areas (5 × 10-6 cm2), and there is some evidence that these areas degrade more than areas without defects.
Mobility Improvement Mechanism in a-Si:H TFTs With Smooth a-Si:H/SiNx Interface
Authors: Takechi K. , Uchida H. , Kaneko S. 
Published: March 2011

ABSTRACTThe authors have investigated the mechanism for mobility improvement in a-Si:H TFTs with smooth a-Si:H/SiNx interface. SiNx surface roughness was evaluated by Atomic Force Microscope (AFM) measurement with nanometer resolution. The properties for a-Si:H initial growth layer near the a-Si:H/SiNx interface are affected by the SiNx surface roughness. By realizing a smooth SiNx surface, the properties for a-Si:H initial growth layer have been improved and high mobility TFT has been obtained. This high mobility TFT will have a great impact in application to high resolution liquid crystal displays.
Effects of Ultraviolet Radiation on the Characteristics of Hydrogenated Amorphous Silicon Thin Film Transistors
Authors: Lee Seong K. , Park Jin S. , Kim Yong S. , Hwang Jung R. , Oh Chang H. , Han Min K. 
Published: March 2011

ABSTRACTThe experimental results regarding to the effects of ultraviolet (UV) light illumination on the characteristics of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT's) have been presented. The device parameters of a-Si:H TFT, such as threshold voltage, field-effect mobility, and subthreshold slope, have been degraded by electrical stress and visible light illumination, but substantially improved by UV radiation. This may be attributed to an annealing effect on the dangling-bond defects, involving a number of phonons generated by absorption of high energy UV photons in the a-Si:H TFT channel. It has been also observed that the off-current of a-Si:H TFT decreases remarkably while the on-current changes very little. From the experimental results, we report that the improved on/off current ratio of a-Si:H TFT may be achieved by UV radiation.
Si Surface Preparation: The Effect of Small Amounts of Carbon Contamination and Sputter Induced Surface Roughness
Authors: Baikie Iain D. 
Published: March 2011

ABSTRACTThe sputter-anneal cleaning process is one of the most common methods of producing clean, defect free, crystalline Si surfaces. However the effects of small amounts of residual Carbon, probably the most insidious surface contaminant, and of Inhomogeneities in the sputter profile have not been investigated in any detail.Using a very high resolution Kelvin probe coupled with Auger Electron Spectroscopy (AES), we have followed the changes in work function, together with surface contaminants, throughout the cleaning process. We show that very small amounts of surface carbon contamination, at or about the AES detection limit, lead to a significant increase in work function of the “Clean surface”. Further as little as 0.6% Carbon substantially influences the initial stages of oxidation of the Si(111) 7×7 surface by (i) hindering formation of the elementary dipole layer and (ii) enhancing oxygen penetration through the surface layer into deeper layers.We have also measured work function profiles of a Si(111) 7×7 sample during sputtering. Inhomogeneities in the sputter profile, particularly around the periphery, are clearly evident and produce variations in work function of some 200 meV across the specimen. Repeated sputter-anneal cycles lead to a degree of disorder in these regions and this is reflected in a different oxidation behaviour.We conclude that work function measurements are both simple to perform and can be utillsed to determine the presence of surface contamination and roughness. As the oxide layer thickness in MOS devices continues to diminish the detection and elimination of residual Carbon contamination will play an ever increasing role in determining device performance. The Kelvin probe can be used at elevated temperatures and pressures and has potential applications in alternative surface cleaning methods including flash annealing and chemical preparations.
Crystal Originated Singularities on Silicon Wafers After SC1 Cleaning
Authors: Morita E. , Ryuta J. , Tanaka T. , Shimanuki Y. 
Published: March 2011

ABSTRACTIt is shown that a new type of singularity is formed on Si wafer surface by the Standard Cleaning 1 (SC1) of the RCA cleaning process″. Such singularities are perceived by laser particle counters as small particles on wafers. It is revealed that the singularities correspond to small shallow pits caused by the etching effect of the SCI cleaning solution. The origin of the pits seems to be some kind of defects in the melt–grown Si crystals. The authors named such “particles” as crystal originated “particles” (COPs).The size–distribution of COPs after single SC1 cleaning cycle is estimated on the basis of variation in the number of COPs with the repeated cleaning cycles. It is revealed that the crystal pulling rate affects the size distribution of COPs. As the pulling rate becomes faster, COP becomes larger in number. From the total number of COPs after the first cleaning cycle and the etching depth, the volume density of origin of COPs can be estimated. The results show that, as the pulling rate becomes faster, the volume density of origin of COPs increases.
Surface Electronic States of Low Temperature H-plasma Cleaned Si(100) and Ge(100) Surfaces
Authors: Cho Jaewon , Schneider T.P. , Nemanich R.J. 
Published: March 2011

ABSTRACTThe surfaces of Si(100) and Ge(100), cleaned at low temperatures by H-plasma, were studied by Angle Resolved UV-Photoemission Spectroscopy(ARUPS). In the case of Si(100), H-plasma exposure produced ordered H-terminated crystallographic structures with either a 2×1 or 1×1 LEED pattern while for Ge(100) a weak H-terminated 2x1 pattern was obtained. The hydride phases, found on the surfaces of the cleaned Si(100), were shown to depend on the temperature of the surface during H-plasma cleaning. The electronic states for the monohydride and dihydride phases were identified by ARUPS. When the plasma cleaned surface was annealed, the phase transition from the dihydride to monohydride was observed. For the Ge(100) surface, an ordered 2x1 monohydride phase was obtained from the surface cleaned at 180°C. After plasma exposure at ≤170°C a 1×1 surface was observed, but the ARUPS indicated that the surface was predominantly composed of disordered monohydride structures. After annealing above the H-dissociation temperatures, the dangling bond surface states were identified for both Si and Ge. The Si(100) and Ge(100) ARUPS spectra shifted after annealing, indicating that the H-terminated surfaces were unpinned.
Silicon Surface Cleaning by A Plasma in Afterglow
Authors: Charlet B. , Peccoud L. 
Published: March 2011

ABSTRACTMicrowave plasma surface cleaning opens an interesting possibility for thin layer preparation. We have investigated the effect of hydrogen and NF3plasma induced by a microwave source. The sample is exposed in the downstream region achieved by a plenum. The cleaning process has been applied to a silicon (100) substrate. The cleaned surface has been analyzed by different methods of investigation: HRTEM, XPS, Therma-Wave and MOS capacitor (C-V) characteristics. The HRTEM observations show a defect-free interface, between the hydrogen cleaned silicon surface and the thermal oxide grown immediately after cleaning. In addition, the silicon crystalline network is not perturbed by induced defects. This was confirmed by Thermal Wave measurements which gave an excellent surface qualification.
Analysis of Plasma Oxidised Hg1-xCdxTe Surfaces
Authors: Leech P.W. , Moore R.L. , Crisman E.E. , Roberts C.B. , Stiles P.J. 
Published: March 2011

ABSTRACTWe report for the first time on the application of Field Enhanced Plasma Oxidation (FEPO) to the passivation of Hg1-xCdxTe. Oxide layers of thickness 250-500Å were grown on Hg0.4Cd0.6Te at temperatures in the range from 30°C to 100°C. The index of refraction of the oxide layer, as determined by ellipsometry, was between 1.99 and 2.10. Auger depth profiles of the surfaces showed a compositional variation through the oxide with predominantly a mix of Cd and Te oxides in a film depleted in Hg. The oxides had dielectric constants of 3.6 to 4.5, and dielectric strength greater than 1 × 107 V/cm. The oxide/semiconductor interfaces had high densities of “slow” states but were capable of being depleted and accumulated.
MOCVD Growth of GaAs on Si with Low Temperature Preheating Process
Authors: Takagi N. , Eshita T. , Miyagaki S. , Kimura M. , Takasaki K. 
Published: March 2011

ABSTRACTA low temperature preheating process is developed for metalorganic chemical vapor deposition (MOCVD) growth of GaAs on wet chemical pretreated Si substrates. NH4 OH/H2 O2 is found to be most effective in decreasing the preheating temperature among the chemicals we tried: NH4 OH/H2 O2, H2SO4 /H2O2, or hot HNO3. By using NH4OH/H2 O2, the preheating temperature is reduced from 1000°C to 875°C. X-ray diffraction measurements and surface observations with an atomic force microscope (AFM) show that the GaAs film quality obtained with the 875 °C preheating process is better than that obtained with 1000°C preheating.
Chemical Structures of Native Oxides Formed During Wet Chemical Treatments on NH4F Treated Si(111) Surfaces
Authors: Hattori Takeo , Ogawa Hiroki 
Published: March 2011

ABSTRACTChemical structures of native oxides formed during wet chemical treatments on NH4F treated Si(111) surfaces were investigated using X-ray Photoelectron Spectroscopy (XPS) and Fourier Transformed Infrared Attenuated Total Reflection(FT-IR-ATR). It was found that the amounts of Si-H bonds in native oxides and those at native oxide/silicon interface are negligibly small in the case of native oxides formed in H2SO4-H2O2-H2O solution. Based on this discovery, it was confirmed that native oxides can be characterized by the amount of Si-H bonds in native oxides. Furthermore, it was found that the combination of various wet chemical treatments with the treatment in NH4OH-H2O2-H2O solution results in the drastic decrease in the amount of Si-H bonds in native oxides.
Surface Contamination Level of GaAs Wafers Treated with Solutions of Organic Base Measured by Total Reflection X-Ray Fluorescence (TXRF)
Authors: Shibaya H. , Kondo H. , Tomizawa K. 
Published: March 2011

ABSTRACTContamination level of chemically cleaned (100) GaAs wafer surfaces were measured by Total reflection X-Ray Fluorescence (TXRF). Cu and Zn were detected as major metallic Impurities on GaAs surfaces. The Cu contamination level was in the range of 1011 atoms/cm2 on wafers treated with NH4 OH/H2O2 /H2O (80:1:400) mixture. On the other hand, Cu could be reduced to less than 5×1010 atoms/cm2 and Zn could be controlled below the detection limit by treating with a choline/H2O2 /H20/Na5P3O10 or SEMICO-CLEAN 23/H2O2 /Na5P3O10 solution. Surface cleanliness depended on the H2O2 concentration and whether or not Na5P3O10 was present in the organic base solutions.
Interaction of Metallic Impurities Adsorbed on Si Wafers in SC1 Solution
Authors: Okuda Hitoshi , Ryuta Jiro , Morita Eturo , Shimanuki Yasushi 
Published: March 2011

ABSTRACTChanges in the surface concentration of Fe, Ni, Cu and Zn on Si wafers processed in a NH 4OH / H2O2 / H2O (SC1) solution was investigated. The adsorption of Fe or Zn on Si wafers was not affected by the other impurities in the SC1 solution. However, the adsorption of Ni or Cu on Si wafers was obstructed by Fe, and was not obstructed by Zn.
A Photoemission Study of Electrochemically Etched Light Emitting Silicon
Authors: Terry Jeff , Liu H. , Cao R. , Woicik J. C. , Pianetta P. , Yang X. , Wu J. , Richter M. , Maluf N. , Pease F. , Dillon A. , Robinson M. , George S. 
Published: March 2011

ABSTRACTThe valence band and the Si 2p core level of electrochemically etched light emitting porous silicon samples prepared with different etching parameters and upon thermal annealing have been studied. The core level shows appreciable broadening as chemical etching time increases. Upon annealing, the core level linewidth decreases and the valence band develops spectral features. The photoluminescence intensity, also, decreases upon annealing. However, impurity species are found to be present only in trace amounts. Our data is consistent with a photoluminescence mechanism involving a silicon species that degrades, decomposes, or desorbs upon annealing.
Characterization of HF Treated (100) Si Surfaces by Surface Charge Analysis (SCA)
Authors: Fitch Jon T. 
Published: March 2011

ABSTRACTSurface Charge Analysis (SCA), and ellipsometry have been used to study the stability over time of HF treated (100) silicon surfaces as a function of the post-HF rinse time. Using SCA, the electrical properties of the chemical terminating layer of these silicon surfaces were measured. The surfaces which remained native oxide free the longest (−10 hours) had very low Qox and Dit values on the order of 1.0 × 1011/cm2 and 5.0 × 1010 eV−lcm−2, respectively. A good correlation was found between Dit and the native oxide thickness measured by ellipsometry. This and other results are discussed in terms of the chemical bonding on the silicon surfaces.