Low Defect Density Microcrystalline-Si Deposited by the Hot Wire Technique

1998 ◽  
Vol 507 ◽  
Author(s):  
A. H. Mahan ◽  
M. Vanecek ◽  
A. Poruba ◽  
V. Vorlicek ◽  
R. S. Crandall ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Defect Density ◽  
Structural Data ◽  
Hot Wire ◽  
Very High Frequency ◽  
Deposition Parameters ◽  
Optical And Electronic Properties ◽  
High Filament ◽  
Si Films ◽  
Substrate Temperatures

ABSTRACTThe optical and electronic properties of a series of microcrystalline silicon (μ-Si) films, deposited by the hot wire (HW) technique, are reported. Preliminary results suggest, using moderate H2 /SiH4 dilution ratios and substrate temperatures (320°C), high filament temperatures, and no H gas purifier, that the subgap absorption for these films, measured using the constant photocurrent (CPM) method, can be as low as that obtained for films deposited by the very high frequency glow discharge (VHF-GD) technique. The film dark conductivities of the HW samples, ranging as low as 2.0 × 10−8 (ohm cm)−1, lend further credance to these low defect values. At the same time, the optical absorption in the region > 1.6 eV is higher than that previously observed for the VHF-GD deposited samples. The present results, discussed in the context of the film microcrystalline fraction, suggest that there is no unique, good quality, low defect density μ-Si material, and that different deposition techniques can be used to successfully deposit device quality gc-Si. We also present optical and structural data for films deposited at lower substrate temperatures and higher deposition rates, and suggest combinations of deposition parameters to be used that may further improve the electronic properties of these films.

Growth and Electronic Properties in Hot Wire Deposited Nanocrystalline Si Solar Cells

2007 ◽  
Vol 989 ◽  
Author(s):  
Kamal Muthukrishnan ◽  
Vikram Dalal ◽  
Max Noack
Keyword(s):  
Electronic Properties ◽  
Defect Density ◽  
Grain Structure ◽  
Degree Of Crystallinity ◽  
Hot Wire ◽  
High Hydrogen ◽  
Filament Temperature ◽  
Random Nucleation ◽  
Hydrogen Dilution ◽  
High Filament

AbstractWe report on the growth and properties of nanocrystalline Si:H grown using a remote hot wire deposition system. Unlike previous results, the temperature of the substrate is not significantly affected by the hot filament in our system. The crystallinity of the growing film and the type of grain structure was systematically varied by changing the filament temperature and the degree of hydrogen dilution. It was found that high hydrogen dilution gave rise to random nucleation and <111> grain growth, whereas lower hydrogen dilution led to preferable growth of <220> grains. Similarly, a high filament temperature gave rise to preferential <111> growth compared to lower filament temperature. The electronic properties such as defect density and minority carrier diffusion length were studied as a function of the degree of crystallinity. It was found that the lowest defect density was obtained for a material which had an intermediate range of crystallnity, as determined from the Raman spectrum. Both highly amorphous and highly crystalline materials gave higher defect densities. The diffusion lengths were measured using a quantum efficiency technique, and were found to be the highest for the mid-range crystalline material. The results suggest that having an amorphous tissue surrounding the crystalline grain helps in passivating the grain boundaries.

Deposition of Polysilicon Films by Hot-Wire CVD at Low Temperatures for Photovoltaic Applications

1995 ◽  
Vol 377 ◽  
Author(s):  
J. Puigdollers ◽  
J. Bertomeu ◽  
J. Cifre ◽  
J. Andreu ◽  
J. C. Delgado
Keyword(s):  
Gas Phase ◽  
Chemical Vapor ◽  
Hot Wire ◽  
Amorphous Phases ◽  
Photovoltaic Applications ◽  
Polysilicon Films ◽  
Hydrogen Mixtures ◽  
Si Films ◽  
Substrate Temperatures ◽  
Very High

ABSTRACTPolysilicon (poly-Si) thin films have been obtained using hot-wire chemical vapor deposition (HWCVD) from silane-hydrogen mixtures. The films were prepared at low substrate temperatures (down to 200°C) and at very high deposition rates (up to 40 Å/s). They showed good crystalline properties and no amorphous phases were detected. The films can also be efficiently doped by adding diborane or phosphine to gas phase. In this paper, an overview of the properties of the poly-Si films, intrinsic and p and n-doped, deposited at our laboratory by HWCVD is presented and discussed. The properties of the material and the features of the deposition technique which are interesting for their application in photovoltaics are emphasized.

Microcrystalline Silicon for Solar Cells at High Deposition Rates by Hot Wire Cvd

2002 ◽  
Vol 715 ◽  
Author(s):  
R. E. I. Schropp ◽  
Y. Xu ◽  
E. Iwaniczko ◽  
G. A. Zaharias ◽  
A. H. Mahan
Keyword(s):  
Solar Cells ◽  
Substrate Temperature ◽  
Volume Fraction ◽  
Silicon Layer ◽  
Hot Wire ◽  
Crystalline Volume Fraction ◽  
Microcrystalline Silicon ◽  
Deposition Rates ◽  
Deposition Parameters ◽  
Si Films

AbstractWe have explored which deposition parameters in Hot Wire CVD have the largest impact on the quality of microcrystalline silicon (μc-Si) made at deposition rates (Rd) < 10 Å/s for use in thin film solar cells. Among all parameters, the filament temperature (Tfil) appears to be crucial for making device quality films. Using two filaments and a filament-substrate spacing of 3.2 cm, μc-Si films, using seed layers, can be deposited at high Tfil (∼2000°C) with a crystalline volume fraction < 70-80 % at Rd's < 30 Å/s. Although the photoresponse of these layers is high (< 100), they appear not to be suitable for incorporation into solar cells, due to their porous nature. n-i-p cells fabricated on stainless steel with these i-layers suffer from large resistive effects or barriers, most likely due to the oxidation of interconnected pores in the silicon layer. The porosity is evident from FTIR measurements showing a large oxygen concentration at ∼1050 cm-1, and is correlated with the 2100 cm-1 signature of most of the Si-H stretching bonds. Using a Tfil of 1750°C, however, the films are more compact, as seen from the absence of the 2100 cm-1 SiH mode and the disappearance of the FTIR Si-O signal, while the high crystalline volume fraction (< 70-80 %) is maintained. Using this Tfil and a substrate temperature of 400°C, we obtain an efficiency of 4.9 % for cells with a Ag/ZnO back reflector, with an i-layer thickness of only ∼0.7 μm. High values for the quantum efficiency extend to very long wavelengths, with values of 33 % at 800 nm and 15 % at 900 nm, which are unequalled by a-SiGe:H alloys. Further, by varying the substrate temperature to enable deposition near the microcrystalline to amorphous transition (‘edge’) and incorporating variations in H2 dilution during deposition of the bulk, efficiencies of 6.0 % have been obtained. The Rd's of these i-layers are 8-10 Å/s, and are the highest to date obtained with HWCVD for microcrystalline layers used in cells with efficiencies of ∼6 %.

Relation between Electronic Properties and Density of Crystalline Agglomerates in Microcrystalline Silicon

2007 ◽  
Vol 989 ◽  
Author(s):  
Paula C.P. Bronsveld ◽  
Arjan Verkerk ◽  
Tomas Mates ◽  
Antonin Fejfar ◽  
Jatindra K. Rath ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Chemical Vapour ◽  
Very High Frequency ◽  
Silicon Thin Films ◽  
High Frequency Plasma ◽  
Frequency Plasma ◽  
Different Types ◽  
Substrate Temperatures ◽  
Intergrain Boundaries ◽  
Very High

AbstractA series of silicon thin films was made by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at substrate temperatures below 100 °C at different hydrogen to silane dilution ratios. The electronic properties of these layers were studied as a function of the surface crystalline fraction as determined accurately from a combination of microscope images at different length scales (gathered by using different types of microscopes). The results show that the electrical conductivity increases monotonously as a function of crystalline surface coverage and no discontinuity is observed at the percolation threshold. An increase in conductivity of four orders of magnitude for layers with a high crystalline content is observed after annealing at temperatures up to 170 °C. Combined with the information that oxygen is incorporated at Si-H surface bond sites, this suggests that doping of the intergrain boundaries by oxygen might be dominantly responsible for the electronic properties of mixed phase silicon.

Deposition of Device Quality μc-Si Films and Solar Cells at High Rates by HWCVD in a W Filament Regime where W/Si Formation is Minimal

2003 ◽  
Vol 762 ◽  
Author(s):  
E. Iwaniczko ◽  
A.H. Mahan ◽  
B. Yan ◽  
L.N. Gedvilas ◽  
D.L. Williamson ◽  
...  
Keyword(s):  
Solar Cells ◽  
Chamber Pressure ◽  
Silicide Formation ◽  
Hot Wire ◽  
Tungsten Filament ◽  
Tandem Solar Cells ◽  
Filament Temperature ◽  
Deposition Parameters ◽  
Si Films ◽  
Filament Surface

Abstractμc-Si has traditionally been deposited by Hot Wire CVD at a low filament temperature. At these temperatures, silicides rapidly form on the filament surface, leading in the case of a tungsten filament to both film reproducibility and filament lifetime issues. By depositing films consecutively using identical deposition parameters, these issues are chronicled for a filament temperature of ∼ 1750°C. Upon increasing the filament temperature to ∼1825-1850°C, these reproducibility and lifetime issues disappear and, by lowering both the substrate temperature and chamber pressure, device quality μc-Si is deposited at high deposition rates in a filament regime where tungsten silicide formation is minimal. Both single junction and tandem solar cells are fabricated using this material, confirming the validity of this approach.

Substrate Temperature Dependence of the Optical and Electronic Properties of Glow Discharge Produced a-Ge:H

1989 ◽  
Vol 149 ◽  
Author(s):  
Yuan- Min Li ◽  
Warren A. Turner ◽  
Choochon Lee ◽  
William Paul
Keyword(s):  
Glow Discharge ◽  
Substrate Temperature ◽  
Temperature Dependence ◽  
Electronic Properties ◽  
Dark Conductivity ◽  
Index Of Refraction ◽  
Atmospheric Contamination ◽  
Optical And Electronic Properties ◽  
Substrate Temperatures ◽  
Post Deposition

ABSTRACTGlow discharge a-Ge:H films produced at substrate temperatures (Tδ) between 50°C and 350°C, with and without a top a-Si:H capping layer, have been studied. The uncapped samples produced at Tδ < 250°C suffer severe post-deposition atmospheric contamination, resulting in orders of magnitude of unstable increase in both the photoresponse and dark conductivity. The capped samples, which have very much reduced immediate post-deposition contamination, show only small increases in the efficiency-mobility-lifetime product (ŋμτ) with increasing Tδ. This contrasts with the results of earlier similar studies on uncapped samples, which showed a peak in either the photoconductivity1 or the ratio of photoconductivity to dark conductivity2 for 150°C < Tδ < 2000C. We have also observed a decrease in the bandgap, a narrowing of the band-tails, an increase in the index of refraction, and a reduction of hydrogen content of the films with increasing Tδ.

Electronic Properties of Hot-Wire Deposited Nanocrystalline Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
R. Brüggemann ◽  
A. Hierzenberger ◽  
H.N. Wanka ◽  
M.B. Schubert
Keyword(s):  
Band Gap ◽  
Electronic Properties ◽  
Defect Density ◽  
High Vacuum ◽  
Sudden Change ◽  
Nanocrystalline Silicon ◽  
Dark Conductivity ◽  
Ultra High Vacuum ◽  
Hot Wire ◽  
Tauc Plot

ABSTRACTWe compare the electronic properties of nanocrystalline silicon from hot-wire chemical vapor deposition in a high-vacuum and an ultra-high-vacuum deposition system, employing W and Ta as filament material. From the constant photocurrent method we identify a band gap around 1.15 eV while, in contrast, a Tauc plot from optical transmission data guides to a wide band gap above 1.9 eV. The sudden change-over from nanocrystalline to amorphous structure in a hydrogen dilution series is also find in the dark and photoconductivity measurements. The samples show a metastability effect in the dark conductivity upon annealing in vacuum with an increase in the dark conductivity, with the large dark conductivity decreasing slowly after the annealing cycle when the cryostat is flushed with air. We identify larger values for the mobility-lifetime products, which corresponds to the smaller defect density shoulder in constant photocur- rent spectra, for the ultra-high-vacuum deposited material compared to the high-vacuun counterpart.

The Determination of Optoelectronic Properties of Microcrystalline andAmorphous Silicon Films

2001 ◽  
Vol 664 ◽  
Author(s):  
Marinus Kunst ◽  
Susanne von Aichberger ◽  
Wilhelm Thom ◽  
Frank Wünsch
Keyword(s):  
Electronic Properties ◽  
Optoelectronic Properties ◽  
Silicon Films ◽  
Hot Wire ◽  
Laser Crystallization ◽  
Carrier Trapping ◽  
Transient Photoconductivity ◽  
Si Films

ABSTRACTThe study and characterization of the (opto)electronic properties of a-Si:H and µSi filmsby contactless transient photoconductivity measurements is presented. The importance ofminority carrier trapping is shown for the example of a-Si:H films prepared with different dopinglevels. It is shown that the microwave mobility determined by these measurements is a versatiletool for the characterization of the films. Examples are given by the study of µ Si filmsproduced by laser crystallization of a-Si:H films and the optimization of the substratetemperature for the Hot Wire deposition of µ Si films.

Deposition of Device Quality μc-Si Films and Solar Cells at High Rates by HWCVD in a W Filament Regime where W/Si Formation is Minimal

2003 ◽  
Vol 762 ◽  
Author(s):  
E. Iwaniczko ◽  
A.H. Mahan ◽  
B. Yan ◽  
L.N. Gedvilas ◽  
D.L. Williamson ◽  
...  
Keyword(s):  
Solar Cells ◽  
Chamber Pressure ◽  
Silicide Formation ◽  
Hot Wire ◽  
Tungsten Filament ◽  
Tandem Solar Cells ◽  
Filament Temperature ◽  
Deposition Parameters ◽  
Si Films ◽  
Filament Surface

Abstractμc-Si has traditionally been deposited by Hot Wire CVD at a low filament temperature. At these temperatures, silicides rapidly form on the filament surface, leading in the case of a tungsten filament to both film reproducibility and filament lifetime issues. By depositing films consecutively using identical deposition parameters, these issues are chronicled for a filament temperature of ∼ 1750°C. Upon increasing the filament temperature to ∼ 1825-1850°C, these reproducibility and lifetime issues disappear and, by lowering both the substrate temperature and chamber pressure, device quality μc-Si is deposited at high deposition rates in a filament regime where tungsten silicide formation is minimal. Both single junction and tandem solar cells are fabricated using this material, confirming the validity of this approach.

The Effect of Hydrogen Dilution of the Gas Plasma on Glow Discharge a-Ge:H

1989 ◽  
Vol 149 ◽  
Author(s):  
W. A. Turner ◽  
S. J. Jones ◽  
Choochon Lee ◽  
S. M. Lee ◽  
Yuan-min Li ◽  
...  
Keyword(s):  
Glow Discharge ◽  
Electronic Properties ◽  
Silicon Germanium ◽  
Alloy System ◽  
Hydrogenated Silicon ◽  
Hydrogen Dilution ◽  
Gas Plasma ◽  
Deposition Parameters ◽  
Optical And Electronic Properties ◽  
Germanium Alloy

ABSTRACTA series of films of amorphous hydrogenated germanium has been produced using the r.f. glow discharge technique by varying the H2/GeH4 ratio in the gas plasma from 0 to 50 while keeping all other deposition parameters constant. Electronic, optical, and structural characterization has been performed. No significant changes in optical and electronic properties were observed for this range of dilution, in contrast to repeated reports on the hydrogenated silicon-germanium alloy system. However, small systematic changes in structure are observed using TEM techniques. We conclude that the observed differences are unimportant in determining the optical and electronic properties of this material.

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