The Influence of Hydrogen Dilution and Substrate Temperature in Hot-Wire Deposition of Amorphous and Microcrystalline Silicon With Filament Temperatures Between 1900 And 2500 °C

1996 ◽  
Vol 420 ◽  
Author(s):  
J. P. Conde ◽  
P. Brogueira ◽  
R. Castanha ◽  
V. Chu
Keyword(s):  
Substrate Temperature ◽  
Growth Rates ◽  
Chemical Vapor ◽  
High Growth ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Crystalline Fraction ◽  
Lower Growth ◽  
Filament Temperature ◽  
Hydrogen Dilution

AbstractThe effect of hydrogen dilution and substrate temperature on the optoelectronic and structural properties of thin films deposited by hot-wire chemical vapor deposition with filament temperatures between 1900 and 2500 °C from silane and hydrogen are studied. Amorphous silicon films are obtained at high deposition rates for hydrogen dilutions below 90%. The deposition rate scales approximately linearly with the filament temperature in this regime. Microcrystalline films are obtained for hydrogen dilution above 90%, independently of the filament temperature and substrate temperature, with much lower growth rates. The Raman spectrum of these films shows high crystalline fraction and small grain size. High conductivity films, typical of microcrystalline silicon, with high growth rates were achieved by either increasing the substrate temperature at low hydrogen dilution, or by using a hydrogen dilution just at the amorphous to microcrystalline transition point.

Amorphous-to-Microcrystalline Silicon Transition in Hot-Wire Chemical Vapor Deposition

1995 ◽  
Vol 377 ◽  
Author(s):  
P. Brogueira ◽  
V. Chu ◽  
J. P. Conde
Keyword(s):  
Thin Films ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Crystalline Fraction ◽  
Hydrogen Dilution ◽  
Process Pressure ◽  
Silicon Growth

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.

Characterization of Microcrystalline Transition from Amorphous Silicon as a Function of Hydrogen Dilution and Substrate Temperature of Hot-wire CVD

2002 ◽  
Vol 715 ◽  
Author(s):  
Keda Wang ◽  
Haoyue Zhang ◽  
Jian Zhang ◽  
Jessica M. Owens ◽  
Jennifer Weinberg-Wolf ◽  
...  
Keyword(s):  
Substrate Temperature ◽  
Sudden Change ◽  
Chemical Vapor ◽  
Threshold Value ◽  
Ir Absorption ◽  
Sudden Increase ◽  
Hot Wire ◽  
Hydrogen Dilution ◽  
Integral Absorption ◽  
Two Peaks

Abstracta-Si:H films were prepared by hot wire chemical vapor deposition. One group was deposited at a substrate temperature of Ts=250°C with varied hydrogen-dilution ratio, 0<R<10; the other group was deposited with fixed R=3 but a varied Ts from 150 to 550°C. IR, Raman and PL spectra were studied. The Raman results indicate that there is a threshold value for the microstructure transition from a- to μc-Si. The threshold is found to be R ≈ 2 at Ts = 250°C and Ts ≈ 200°C at R=3. The IR absorption of Si-H at 640 cm-1 was used to calculate the hydrogen content, CH. CH decreased monotonically when either R or Ts increased. The Si-H stretching mode contains two peaks at 2000 and 2090 cm-1. The ratio of the integral absorption peaks I2090/(I2090+I2090) showed a sudden increase at the threshold of microcrystallinity. At the same threshold, the PL features also indicate a sudden change from a- to μc-Si., i.e. the low energy PL band becomes dominant and the PL total intensity decreases. We attribute the above IR and PL changes to the contribution of microcrystallinity, especially the c-Si gain-boundaries.

Guiding Principle to Develop Intrinsic Microcrystalline Silicon Absorber Layer For Solar Cell By Hot-Wire Cvd

2001 ◽  
Vol 664 ◽  
Author(s):  
A. R. Middya ◽  
U. Weber ◽  
C. Mukherjee ◽  
B. Schroeder
Keyword(s):  
Growth Rate ◽  
Solar Cell ◽  
Cell Structure ◽  
Short Circuit ◽  
Chemical Vapor ◽  
High Growth ◽  
High Growth Rate ◽  
Open Circuit ◽  
Hot Wire ◽  
Microcrystalline Silicon

ABSTRACTWe report on ways to develop device quality microcrystalline silicon (μc-Si:H) intrinsic layer with high growth rate by hot-wire chemical vapor deposition (HWCVD). With combine approach of controlling impurities and moderate H-dilution [H2/SiH4 ͌ 2.5], we developed, for the first time, highly photosensitive (103 μc-Si:Hfilms with high growth rate (>1 nm/s); the microstructure of the film is found to be close to amorphous phase (fc ͌ 46 ̻± 5%). The photosensitivity systematically decreases with fc and saturates to 10 for fc> 70%. On application of these materials in non-optimized pin [.proportional]c-Si:H solar cell structure yields 700 mV open-circuit voltage however, surprisingly low fill factor and short circuit current. The importance of reduction of oxygen impurities [O], adequate passivation of grain boundary (GB) as well as presence of inactive GB of (220) orientation to achieve efficient [.proportional]c-Si:H solar cells are discussed.

Increase of Hydrogen-Radical Density and Improvement of The Crystalline Volume Fraction of Microcrystalline Silicon Films Prepared by Hot-Wire Assisted Pecvd Method

2000 ◽  
Vol 609 ◽  
Author(s):  
Norimitsu Yoshida ◽  
Takashi Itoh ◽  
Hiroki Inouchi ◽  
Hidekuni Harada ◽  
Katsuhiko Inagaki ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Chemical Vapor ◽  
Rf Plasma ◽  
Hot Wire ◽  
Dilution Ratio ◽  
Microcrystalline Silicon ◽  
Hydrogen Dilution ◽  
Hydrogen Radical ◽  
Hydrogen Radicals ◽  
Hydrogenated Amorphous

ABSTRACTHigher crystalline Si volume fractions in hydrogenated microcrystalline silicon ( µc-Si:H) films have been achieved by the hot-wire assisted plasma enhanced chemical vapor deposition (HWA-PECVD) method compared with those in films by conventional PECVD. µc-Si:H films can also be prepared by HWA-PECVD under typical conditions used for preparing hydrogenated amorphous silicon (a-Si:H) films by PECVD, in which the hydrogen-dilution ratio (H2 / SiH4) is ∼ 10. The hot wire seems to produce hydrogen radicals. As a result, the HWA- PECVD method can control hydrogen-radical densities in the RF plasma, and this method can also control the ratio of hydrogen coverage at the surface of the film.

Structural and optoelectronic properties of amorphous and microcrystalline silicon deposited at low substrate temperatures by RF and HW CVD

1999 ◽  
Vol 557 ◽  
Author(s):  
P. Alpuim ◽  
V. Chu ◽  
J. P. Conde
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Defect Density ◽  
Chemical Vapor ◽  
Optoelectronic Properties ◽  
Microcrystalline Silicon ◽  
Crystalline Fraction ◽  
Hydrogen Dilution ◽  
Structural And Optoelectronic Properties ◽  
Substrate Temperatures

AbstractThe structural and optoelectronic properties of silicon thin films prepared by hot wire chemical vapor deposition and radio frequency plasma enhanced chemical vapor deposition are studied in the range of substrate temperatures (Tsub)from 100 °C to 25 °C. The defect density, structure factor and bond angle disorder of amorphous silicon films (a-Si:H) deposited by both techniques are strongly improved by the use of hydrogen dilution. Correlation of these structural properties with important optoelectronic properties, such as photo-to-dark conductivity ratio, is made. Microcrystalline silicon (μc-Si:H) is obtained using HW with a large crystalline fraction for hydrogen dilutions above 85% independently of Tsub. The deposition of μc-Si:H by RF requires increasing the hydrogen dilution and shows decreasing crystalline fraction as Tsub is decreased. The properties of the low Tsub films are compared to those of samples produced at 175 °C and 250 °C in the same reactors.

Thin Film a-Si/poly-Si Multibandgap Tandem Solar Cells With Both Absorber Layers Deposited by Hot Wire Cvd

2001 ◽  
Vol 664 ◽  
Author(s):  
R.E.I. Schropp ◽  
C.H.M. Van Der Werf ◽  
M.K. Van Veen ◽  
P.A.T.T. Van Veenendaal ◽  
R. Jimenez Zambrano ◽  
...  
Keyword(s):  
Solar Cells ◽  
Substrate Temperature ◽  
Band Gap ◽  
Steel Substrate ◽  
Light Trapping ◽  
Chemical Vapor ◽  
Hot Wire ◽  
Tandem Solar Cells ◽  
Hydrogen Dilution ◽  
P Type

ABSTRACTThe first competitive a-Si/poly-Si multibandgap tandem cells have been made in which the two intrinsic absorber layers are deposited by Hot Wire Chemical Vapor Deposition (HWCVD). These cells consist of two stacked n-i-p type solar cells on a plain stainless steel substrate using plasma deposited n- and p-type doped layers and Hot-Wire deposited intrinsic (i) layers, where the i-layer is either amorphous (band gap 1.8 eV) or polycrystalline (band gap 1.1 eV). In this tandem configuration, all doped layers are microcrystalline and the two intrinsic layers are made by decomposing mixtures of silane and hydrogen at hot filaments in the vicinity of the substrate. For the two layers we used individually optimized parameters, such as gas pressure, hydrogen dilution ratio, substrate temperature, filament temperature, and filament material. The solar cells do not comprise an enhanced back reflector, but feature a natural mechanism for light trapping, due to the texture of the (220) oriented poly-Si absorber layer and the fact that all subsequent layers are deposited conformally. The deposition rate for the throughput limiting step, the poly-Si i-layer, is ≍ 5-6 Å/s. This layer also determines the highest substrate temperature required during the preparation of these tandem cells (500 °C). The initial efficiency obtained for these tandem cells is 8.1 %. The total thickness of the silicon nip/nip structure is only 1.1 µm.

An Absorption Study of Microcrystalline Silicon Deposited by Hot-Wire CVD

1997 ◽  
Vol 467 ◽  
Author(s):  
F. Diehl ◽  
W. Herbst ◽  
B. Schröder ◽  
H. Oechsner
Keyword(s):  
Optical Absorption ◽  
Crystallite Size ◽  
Gas Pressure ◽  
Absorption Enhancement ◽  
Flow Ratio ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Filament Temperature ◽  
Enhanced Absorption ◽  
Hydrogen Dilution

ABSTRACTThe effect of variation of the preparation parameters filament temperature Tfil, gas pressure p and hydrogen dilution (H2/SiH4-flow ratio) on the absorption spectra of microcrystalline silicon deposited by the hot-wire technique (hw-μc-Si:H) has been studied by means of Photothermal Deflection Spectroscopy (PDS). We find an enhanced absorption of the μc-Si:H compared to crystalline silicon in the band gap (defect absorption) as well as in the interband transition region. An increase of absorption has already been reported for μc-Si:H films prepared by different techniques. In the case of hw-pc-Si:H we observe a relation between the absorption enhancement and the crystallite size. Increasing the gas pressure from 35 to 400 mTorr (Tfil=1850°C) or the filament temperature from 1750°C to 1950°C (p=100mTorr) the crystallite sizes, deduced from X-ray diffraction measuements, range from 10 to 60 nm. An alteration of the hydrogen dilution by varying the flow ratio between 2.5 and 25 does not affect the crystallite size and the optical absorption remains constant. In our opinion the enhancement cannot be described by a simple superposition of an amorphous and a crystalline absorption coefficient weighted by the volume fractions of the amorphous and crystalline phase, respectively. The possible reasons for the enhanced absorption will be discussed. The variation of the crystallite size with deposition conditions offers the possibility to control the optical absorption of μc-Si:H which is important for incorporating the material either as window layers or intrinsic layers in solar cells.

Growth Mechanism of Microcrystalline Silicon Deposited by ECRCVD

1996 ◽  
Vol 452 ◽  
Author(s):  
I. Beckers ◽  
E. Conrad ◽  
P. Müller ◽  
N. H. Nickel ◽  
I. Sieber ◽  
...  
Keyword(s):  
Vapor Deposition ◽  
Cyclotron Resonance ◽  
Electron Cyclotron Resonance ◽  
Chemical Vapor ◽  
Growth Mechanisms ◽  
Microcrystalline Silicon ◽  
Crystalline Fraction ◽  
Hydrogen Dilution ◽  
Si Films ◽  
Scanning Electron

AbstractMicrocrystalline silicon (μc-Si) films were prepared by electron cyclotron resonance assisted chemical vapor deposition (ECRCVD) using helium, argon and hydrogen dilution. The crystalline fraction was estimated from Raman backscattering spectra and scanning electron-microscopy (SEM) was used to obtain information on roughness and homogeneity of the films. For hydrogen dilution the highest crystallinity (Xc = 85 %) occurs at a ratio of ΔH = [H2]/([H2]+[SiH4])= 0.98. At the same time the deposition rate decreases continuously with increasing H2 dilution. These results are consistent with the idea that H etching promotes the growth of μc-Si. At ΔH > 0.98 a Xc decreases due to a H mediated transition of small crystallites into amorphous tissue. The implications of these results for the growth mechanisms are discussed.

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