Improved Light Soaking Stability of R.F. Sputter Deposited Amorphous Silicon

1991 ◽  
Vol 219 ◽  
Author(s):  
A. Wynveen ◽  
J. Fan ◽  
J. Kakalios ◽  
J. Shinar
Keyword(s):  
Amorphous Silicon ◽  
Hydrogen Content ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Initial Defect ◽  
Optical Gap ◽  
Sputter Deposited ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous

ABSTRACTStudies of r.f. sputter deposited hydrogenated amorphous silicon (a-Si:H) find that the light induced decrease in the dark conductivity and photoconductivity (the Staebler-Wronski effect) is reduced when the r.f. power used during deposition is increased. The slower Staebler-Wronski effect is not due to an increase in the initial defect density in the high r.f. power samples, but may result from either the lower hydrogen content or the smaller optical gap found in these films.

Low Hydrogen Content, High Quality Hydrogenated Amorphous Silicon Grown by Hot-Wire CVD

1999 ◽  
Vol 557 ◽  
Author(s):  
Brent P. Nelson ◽  
Richard S. Crandall ◽  
Eugene Iwaniczko ◽  
A. H. Mahan ◽  
Qi Wang ◽  
...  
Keyword(s):  
Substrate Temperature ◽  
Amorphous Silicon ◽  
Hydrogen Content ◽  
Defect Density ◽  
Flow Direction ◽  
Scale Up ◽  
Hydrogenated Amorphous Silicon ◽  
Hot Wire ◽  
High Quality ◽  
Hydrogenated Amorphous

AbstractWe grow hydrogenated amorphous silicon (a-Si:H) by Hot-Wire Chemical Vapor Deposition (HWCVD). Our early work with this technique has shown that we can grow a-Si:H that is different from typical a-Si:H materials. Specifically, we demonstrated the ability to grow a-Si:H of exceptional quality with very low hydrogen (H) contents (0.01 to 4 at. %). The deposition chambers in which this early work was done have two limitations: they hold only small-area substrates and they are incompatible with a load-lock. In our efforts to scale up to larger area chambers—that have load-lock compatibility—we encountered difficulty in growing high-quality films that also have a low H content. Substrate temperature has a direct effect on the H content of HWCVD grown a-Si:H. We found that making dramatic changes to the other deposition process parameters—at fixed substrate temperature and filament-to-substrate spacing—did not have much effect on the H content of the resulting films in our new chambers. However, these changes did have profound effects on film quality. We can grow high-quality a-Si:H in the new larger area chambers at 4 at. % H. For example, the lowest known stabilized defect density of a-Si:H is approximately 2 × 1016 cm-3, which we have grown in our new chamber at 18 Å/s. Making changes to our original chamber—making it more like our new reactor—did not increase the hydrogen content at a fixed substrate temperature and filament-to-substrate spacing. We continued to grow high quality films with low H content in spite of these changes. An interesting, and very useful, result of these experiments is that the orientation of the filament with respect to silane flow direction had no influence on film quality or the H content of the films. The condition of the filament is much more important to growing quality films than the geometry of the chamber due to tungsten-silicide formation on the filament.

The Potential of Hydrogenated Amorphous Silicon-Sulfur Alloys for Absorber Materials in Photovoltaic Devices

1996 ◽  
Vol 426 ◽  
Author(s):  
P. C. Taylor ◽  
S. L. Wang
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Optical Excitation ◽  
Dark Conductivity ◽  
General Idea ◽  
Group Vi ◽  
Excitation Light ◽  
Staebler Wronski Effect ◽  
P Type ◽  
Hydrogenated Amorphous

AbstractThe group VI element, sulfur, is an inefficient donor in hydrogenated amorphous silicon (a-Si:H). The compensation by sulfur donors of the p-type conductivity obtained with diborane in a-Si:H provides additional evidence of the role of sulfur as a donor. By adding equal amounts of diborane and hydrogen sulfide in the plasma the dark conductivity at room temperature can be reduced by one to two orders of magnitude compared to the corresponding p-type a-Si:H with the same boron concentration. Unlike phosphorus doping, a portion of the sulfur-related donors is passivated by hydrogen in the annealed state. This passivated portion can be rendered electrically active by optical excitation. This effect is similar to that which has been called persistent photoconductivity (PPC) and occurs in some compensated samples of a-Si:H and in some multilayer structures. The PPC effect has the opposite effect on both the photo- and dark conductivities from the Staebler-Wronski effect. For this reason it is possible to find an appropriate S/Si ratio where the two effects cancel as far as the conductivity is concerned. For an appropriate concentration of S in “intrinsic” a-Si:H one can obtain samples with high photoconductivity and essentially no degradation in either the dark or the photo-conductivities upon prolonged optical excitation (light soaking). These results suggest that at least the majority carriers are unaffected; however, it remains unclear what effect this second metastability will have on the minority carriers, and hence on PV device applications. The general idea that the addition of a second metastability to hydrogenated amorphous silicon (a-Si:H) might counteract the deleterious consequences of the Staebler-Wronski effect is presented.

Stability of hydrogenated amorphous silicon prepared by reactive evaporation

1991 ◽  
Vol 69 (6) ◽  
pp. 679-683
Author(s):  
D. C. Craigen ◽  
R. D. Audas ◽  
D. E. Brodie
Keyword(s):  
Activation Energy ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Dark Conductivity ◽  
Time Curve ◽  
Switching Model ◽  
Order Of Magnitude ◽  
Reactive Gases ◽  
Staebler Wronski Effect ◽  
Hydrogenated Amorphous

Hydrogenated amorphous silicon (a-Si:H) was prepared by evaporating Si in a controlled ambient of reactive gases. Contamination of the samples by exposure to air affects both the dark conductivity and the photoconductivity. Some of the contamination effects can be removed by annealing, but some changes are not reversible. The irreversible changes are mainly due to the chemisorption of oxygen obtained from water vapour when the samples are stored in air. The Staebler–Wronski effect is observed in all samples whose photoconductivity is at least an order of magnitude higher than the dark conductivity. The photoconductivity versus time curve displays at t−1/3 dependence, typical of the Staebler–Wronski effect, but the degradation is much slower than that reported for glow discharge a-Si:H. The activation energy for the effect is 0.12 eV, which is larger than the 0.04 eV expected for the bond-switching model.

The Potential of Hydrogenated Amorphous Silicon-Sulfur Alloys for Absorber Materials in Photovoltaic Devices

1996 ◽  
Vol 420 ◽  
Author(s):  
P. C. Taylor ◽  
S. L. Wang
Keyword(s):  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Optical Excitation ◽  
Dark Conductivity ◽  
General Idea ◽  
Group Vi ◽  
Excitation Light ◽  
Staebler Wronski Effect ◽  
P Type ◽  
Hydrogenated Amorphous

AbstractThe group VI element, sulfur, is an inefficient donor in hydrogenated amorphous silicon (a-Si:H). The compensation by sulfur donors of the p-type conductivity obtained with diborane in a-Si:H provides additional evidence of the role of sulfur as a donor. By adding equal amounts of diborane and hydrogen sulfide in the plasma the dark conductivity at room temperature can be reduced by one to two orders of magnitude compared to the corresponding p-type a-Si:H with the same boron concentration. Unlike phosphorus doping, a portion of the sulfur-related donors is passivated by hydrogen in the annealed state. This passivated portion can be rendered electrically active by optical excitation. This effect is similar to that which has been called persistent photoconductivity (PPC) and occurs in some compensated samples of a-Si:H and in some multilayer structures. The PPC effect has the opposite effect on both the photo- and dark conductivities from the Staebler-Wronski effect. For this reason it is possible to find an appropriate S/Si ratio where the two effects cancel as far as the conductivity is concerned. For an appropriate concentration of S in “intrinsic” a-Si:H one can obtain samples with high photoconductivity and essentially no degradation in either the dark or the photo-conductivities upon prolonged optical excitation (light soaking). These results suggest that at least the majority carriers are unaffected; however, it remains unclear what effect this second metastability will have on the minority carriers, and hence on PV device applications. The general idea that the addition of a second metastability to hydrogenated amorphous silicon (a-Si:H) might counteract the deleterious consequences of the Staebler-Wronski effect is presented.

scholarly journals Numerical Design of Ultrathin Hydrogenated Amorphous Silicon-Based Solar Cell

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
F. X. Abomo Abega ◽  
A. Teyou Ngoupo ◽  
J. M. B. Ndjaka
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Amorphous Silicon ◽  
Buffer Layer ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Theoretical Work ◽  
Silicon Based ◽  
The Impact ◽  
Hydrogenated Amorphous

Numerical modelling is used to confirm experimental and theoretical work. The aim of this work is to present how to simulate ultrathin hydrogenated amorphous silicon- (a-Si:H-) based solar cells with a ITO BRL in their architectures. The results obtained in this study come from SCAPS-1D software. In the first step, the comparison between the J-V characteristics of simulation and experiment of the ultrathin a-Si:H-based solar cell is in agreement. Secondly, to explore the impact of certain properties of the solar cell, investigations focus on the study of the influence of the intrinsic layer and the buffer layer/absorber interface on the electrical parameters ( J SC , V OC , FF, and η ). The increase of the intrinsic layer thickness improves performance, while the bulk defect density of the intrinsic layer and the surface defect density of the buffer layer/ i -(a-Si:H) interface, respectively, in the ranges [109 cm-3, 1015 cm-3] and [1010 cm-2, 5 × 10 13  cm-2], do not affect the performance of the ultrathin a-Si:H-based solar cell. Analysis also shows that with approximately 1 μm thickness of the intrinsic layer, the optimum conversion efficiency is 12.71% ( J SC = 18.95   mA · c m − 2 , V OC = 0.973   V , and FF = 68.95 % ). This work presents a contribution to improving the performance of a-Si-based solar cells.

Reduction of the Defect Density in a-Si:H Deposited at ≤250°C

1993 ◽  
Vol 297 ◽  
Author(s):  
Hitoshi Nishio ◽  
Gautam Ganguly ◽  
Akihisa Matsuda
Keyword(s):  
Diffusion Coefficient ◽  
Amorphous Silicon ◽  
Surface Diffusion ◽  
Film Growth ◽  
Defect Density ◽  
Hydrogenated Amorphous Silicon ◽  
Device Fabrication ◽  
Surface Diffusion Coefficient ◽  
Hydrogenated Amorphous ◽  
Substrate Temperatures

We present a method to reduce the defect density in hydrogenated amorphous silicon (a-Si:H) deposited at low substrate temperatures similar to those used for device fabrication . Film-growth precursors are energized by a heated mesh to enhance their surface diffusion coefficient and this enables them to saturate more surface dangling bonds.

Etching Properties of Hydrogenated Amorphous Silicon

1991 ◽  
Vol 219 ◽  
Author(s):  
Y. S. Tsuo ◽  
Y. Xu ◽  
D. W. Baker ◽  
S.K Deb
Keyword(s):  
Amorphous Silicon ◽  
Plasma Etching ◽  
Hydrogen Content ◽  
Chemical Etching ◽  
Isopropyl Alcohol ◽  
Hydrogen Plasma ◽  
Hydrogenated Amorphous Silicon ◽  
Wet Chemical ◽  
Wet Chemical Etching ◽  
Hydrogenated Amorphous

ABSTRACTWe have studied wet-chemical and dry etching properties of doped and undoped hydrogenated amorphous silicon (a-Si:H) films with bonded hydrogen content varying from 0 to 20 at.%. Etching processes studied include (1) wet-chemical etching using solutions of KOH, isopropyl alcohol (IPA), and H2O, (2) hydrogen plasma etching, and (3) XeF2 vapor etching.

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