Transient Mean-Field Reaction-Diffusion Model Applied to Hydrogen Evolution From Hydrogenated Amorphous Silicon

1995 ◽  
Vol 377 ◽  
Author(s):  
A. J. Franzi ◽  
M. Mavrikakis ◽  
J. W. Schwank ◽  
J. L. Gland
Keyword(s):  
Amorphous Silicon ◽  
Hydrogen Evolution ◽  
Diffusion Model ◽  
Mean Field ◽  
Hydrogenated Amorphous Silicon ◽  
Reaction Diffusion ◽  
Reaction Diffusion Model ◽  
Wide Range ◽  
Field Reaction ◽  
Hydrogenated Amorphous

ABSTRACTHydrogen bulk mobility plays an important role in determining a wide range of materials and electronic properties of hydrogenated amorphous silicon (a-Si:H). The existence of two types of hydrogen traps plays an important role in controlling hydrogen mobility in, and evolution of hydrogen from a-Si:H, however, theoretical and experimental literature values for the trap energetics vary considerably. We have developed a mean-field reaction-diffusion model which explicitly includes two trap states and realistic surface processes to model hydrogen evolution from a-Si:H. Modern numerical techniques were required to solve this challenging problem over the wide range of temperatures and concentrations encountered in typical hydrogen evolution experiments. The model is based on a number of experimentally established parameters. Comparison of our rigorous model with temperature programmed hydrogen evolution experiments provides a powerful method for characterizing the energetics, trap concentrations and diffusivity of hydrogen in a-Si:H.

Role of Hydrogen Microstructure in Amorphous Silicon

1992 ◽  
Vol 258 ◽  
Author(s):  
Sufi Zafar ◽  
E. A. Schiff
Keyword(s):  
Amorphous Silicon ◽  
Hydrogen Evolution ◽  
Hydrogen Diffusion ◽  
Hydrogenated Amorphous Silicon ◽  
Hydrogenated Amorphous ◽  
Unified Description

ABSTRACTA model for correlating the observed properties of hydrogenated amorphous silicon (a-Si:H) with the underlying hydrogen microstructure is reviewed. The model provides a unified description of defect equilibration, hydrogen evolution, rehydrogenation and hydrogen diffusion measurements.

Boron doping in a-SiO:H,

2014 ◽  
Vol 92 (7/8) ◽  
pp. 586-588 ◽  
Author(s):  
Y. Kitani ◽  
T. Maeda ◽  
S. Kakimoto ◽  
K. Tanaka ◽  
R. Okumoto ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Hole Mobility ◽  
Boron Doping ◽  
Type A ◽  
Dark Conductivity ◽  
Wide Range ◽  
P Type ◽  
Hydrogenated Amorphous ◽  
Silicon Oxygen

Boron-doping characteristics in hydrogenated amorphous silicon–oxygen alloys (a-SiO:H) have been studied in contrast to those in hydrogenated amorphous silicon (a-Si:H). Although the boron-incorporation efficiency shows almost the same value between a-SiO:H and a-Si:H, p-type a-SiO:H (p-a-SiO:H) exhibits lower dark conductivity by one or two orders of magnitude as compared to p-type a-Si:H (p-a-Si:H) in a wide range of doping levels. We have found that p-a-SiO:H exhibits low dark conductivity as compared to p-a-Si:H even when we choose samples showing the same activation energy from a variety of as-deposited and thermally annealed samples. We have concluded from the different Urbach-energy values between high quality intrinsic a-SiO:H and a-Si:H that the origin of low dark conductivity in p-a-SiO:H is due to low hole mobility.

Kinetics Of Hydrogen Evolution And Crystallization In Hydrogenated Amorphous Silicon Films Studied By Thermal Analysis And Raman Scattering

1993 ◽  
Vol 321 ◽  
Author(s):  
Nagarajan Sridhar ◽  
D. D. L. Chung ◽  
W. A. Anderson ◽  
W. Y. Yu ◽  
L. P. Fu ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Raman Scattering ◽  
Amorphous Silicon ◽  
Hydrogen Evolution ◽  
Deposition Temperature ◽  
Evolved Gas Analysis ◽  
Silicon Film ◽  
Hydrogenated Amorphous Silicon ◽  
Film Deposition ◽  
Hydrogenated Amorphous

ABSTRACTWe observed the processes of hydrogen evolution and crystallization in hydrogenated Amorphous silicon 0.5–7 μm thick films (deposited by dc glow discharge on Molybdenum) by differential scanning calorimetry (DSC), Raman scattering and thermogravimetric analysis (TGA). Investigation was made as a function of doping, deposition temperature and film thickness. For all the films, an endothermic DSC peak was observed at 694 °C (onset). That this peak was at least partly due to hydrogen evolution was shown by TGA, which showed weight loss beginning at 694 °C, and by evolved gas analysis, which showed hydrogen evolution at 694 °C. This temperature (658–704 °C) increased with increasing heating rate (5–30 °C/min). Doping reduced this temperature from 694 to 625 °C for boron doping and to 675 °C for phosphorous doping. Hydrogen evolution kinetics and FTIR results suggest that the silicon-hydrogen bonding in the intrinsic film was a mixture of SiH and S1H2, and was predominantly SiH in the phosphorous doped films and SiH2 in the boron doped films. Crystallization was independent of silicon-hydrogen bonding in the as-deposited Amorphous silicon film. It was bulk (not interface) induced. No exothermic DSC peak accompanied the crystallization. The film deposition temperature had little effect on the DSC result, but crystallization was enhanced by a higher deposition temperature.

Dependence of Steady-State Defect Density in Hydrogenated Amorphous Silicon on Carrier Generation Rate Studied Over a Wide Range

1993 ◽  
Vol 297 ◽  
Author(s):  
Nobuhiro Hata ◽  
Gautam Ganguly ◽  
Akihisa Matsuda
Keyword(s):  
Steady State ◽  
Amorphous Silicon ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Continuous Light ◽  
Effective Rate ◽  
Defect States ◽  
Carrier Generation ◽  
Wide Range ◽  
Hydrogenated Amorphous

Measurements of the steady-state defect density (Nst) in hydrogenated amorphous silicon under illumination of pulse-laser light, as well as of continuous light, were carried out; and the dependence of Nst on the effective rate of carrier generation (G) is presented. The values of G ranged from 8 x 1021 to 2.4 × 1023 cm-3 s-1, while the illumination temperature was kept at 30 °C or at 105 °C. The results showed trends of Nst increasing with G similarly to the trends in the literature, but covered a higher and wider G range, and fitted a defect model which assumes a limited number of possible defect states.

Photoelectrochemical water splitting by tandem type and heterojunction amorphous silicon electrodes

1988 ◽  
Vol 66 (8) ◽  
pp. 1853-1856 ◽  
Author(s):  
Yuichi Sakai ◽  
Satoshi Sugahara ◽  
Michio Matsumura ◽  
Yoshihiro Nakato ◽  
Hiroshi Tsubomura
Keyword(s):  
Sulfuric Acid ◽  
Amorphous Silicon ◽  
Hydrogen Evolution ◽  
Water Splitting ◽  
Hydrogenated Amorphous Silicon ◽  
Chemical Conversion ◽  
External Bias ◽  
P Type ◽  
Conversion Efficiencies ◽  
Hydrogenated Amorphous

The tandem type hydrogenated amorphous silicon (a-Si) electrode having an [n–i–p–n–i–p] structure and a similar tandem a-Si electrode having [n–i–p–n–i–p–n] layers deposited on p-type crystalline Si showed cathodic photocurrents accompanied by hydrogen evolution starting at potentials 1.67 and 2.08 V, respectively, more positive than the thermodynamic hydrogen evolution potential in a sulfuric acid solution. These electrodes, when connected to an RuO2 counterelectrode, caused sustained water splitting without external bias, giving solar-to-chemical conversion efficiencies of 1.98% and 2.93%, respectively, under simulated AM 1, 100 mW cm−2 solar radiation. These efficiencies are critically compared with the efficiency of another type of solar photoelectrolysis of water, namely, the electrolysis of water by the electrical output from solid-state solar cells.

First-principles Modeling of Structure, Vibrations, Electronic Properties and Bond Dynamics in Hydrogenated Amorphous Silicon: Theory versus Experiment

2009 ◽  
Vol 1153 ◽  
Author(s):  
Anatoli Shkrebtii ◽  
Ihor Kupchak ◽  
Franco Gaspari
Keyword(s):  
Amorphous Silicon ◽  
Electronic Properties ◽  
First Principles ◽  
Hydrogen Diffusion ◽  
Hydrogenated Amorphous Silicon ◽  
Amorphous Structure ◽  
Material Structure ◽  
Electron Charge Density ◽  
Wide Range ◽  
Hydrogenated Amorphous

AbstractWe carried out extensive first-principles modeling of microscopic structural, vibrational, electronic properties and chemical bonding in hydrogenated amorphous silicon (a-Si:H) in a wide range of hydrogen concentration and preparation conditions. The theory has been compared with experimental results to comprehensively characterize this semiconductor material. The computer modeling includes ab-initio Molecular Dynamics (MD), atomic structure optimization, advanced signal processing and computer visualization of dynamics. We extracted parameters of hydrogen and silicon bonding, electron charge density and calculated electron density of states (EDOS) and hydrogen diffusion. A good agreement of the theory with various experiments allowed us to correlate microscopic processes at the atomic level with macroscopic properties. Here we focus on correlation of the amorphous structure of the material, atom dynamics and electronic properties. These results are of increasing interest due to extensive application of a-Si:H in modern research and technology and to the significance of detailed understanding of the material structure, bonding, disordering mechanisms and stability.

Characterization of Gap Defect States in Hydrogenated Amorphous Silicon Materials

2008 ◽  
Vol 1066 ◽  
Author(s):  
Lihong Jiao ◽  
C. R. Wronski
Keyword(s):  
Amorphous Silicon ◽  
Energy Levels ◽  
Hydrogenated Amorphous Silicon ◽  
Defect States ◽  
Wide Range ◽  
Silicon Materials ◽  
Energy Dependent ◽  
Hydrogenated Amorphous ◽  
Dependent Density ◽  
Gap State

ABSTRACTAn enhanced simulation model based on the carrier recombination through these states was developed to characterize the gap defect states in hydrogenated amorphous silicon materials (a-Si:H). The energy dependent density of electron occupied gap states, kN(E), was derived directly from Dual Beam Photoconductivity (DBP) measurements at different bias currents. Through Gaussian de-convolution of kN(E), the energy peaks of the multiple defect states, including both neutral and charged states, were obtained. These energy levels, together with the information on the capture cross sections, were used as known input parameters to self-consistently fit the subgap absorption spectra, the electron mobility-lifetime products over a wide range of generation rates, as well as the energy dependent density of electron occupied gap state spectra. Accurate gap state information was obtained and the nature of the defect states was studied. Simulation results on light degraded hydrogen diluted, protocrystalline a-Si:H show that the density of charged states is 2.3 times that of neutral states. The two states close to the midgap act as effective recombination centers at low generation rates and play key roles in photoconductivity studies.

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