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.

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.

Light scattering and enhanced optical absorption in hot wire microcrystalline silicon

1998 ◽  
Vol 84 (6) ◽  
pp. 3416-3418 ◽  
Author(s):  
F. Diehl ◽  
B. Schröder ◽  
H. Oechsner
Keyword(s):  
Light Scattering ◽  
Optical Absorption ◽  
Hot Wire ◽  
Microcrystalline Silicon

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.

Influence of the H2 Dilution And Filament Temperature on the Properties of P Doped Silicon Carbide Thin Films Produced by Hot-Wire Technique

1998 ◽  
Vol 507 ◽  
Author(s):  
I. Ferreira ◽  
H. Águas ◽  
L. Mendes ◽  
F. Fernandes ◽  
E. Fortunato ◽  
...  
Keyword(s):  
Thin Films ◽  
Silicon Carbide ◽  
Surface Morphology ◽  
Morphological Data ◽  
Hot Wire ◽  
Carbon Incorporation ◽  
Filament Temperature ◽  
Hydrogen Dilution ◽  
Boron Doped ◽  
Doped Silicon

ABSTRACTThis work deals with the role of hydrogen dilution and filament temperature on the morphology, structure and electrical properties of nanocrystalline boron doped silicon carbide thin films produced by hot-wire technique. The structural and morphological data obtained by XRD, SEM and micro-Raman show that for filament temperatures and hydrogen dilutions above 2100°C and 90%, respectively, the surface morphology of the films is granular with a needle shape, while for lower filament temperatures and hydrogen dilutions the surface morphology gets honeycomb like. The SIMS analysis reveals that films produced with filament temperatures of about 2200°C and hydrogen dilution of 99% present a higher hydrogen and carbon incorporation than the films produced at lower temperatures and hydrogen dilutions. These results agree with the electrical and optical characteristics recorded that show that the films produced exhibit optical gaps in the range from 1.8 to 2 eV and transverse conductivities ranging from 10−1S/cm to 10−3 S/cm, consistent with the degree of films crystallinity and carbon incorporation recorded.

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.

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.

The Effect of Hydrogen Dilution on Hot-Wire Thin-Film Transistors

1998 ◽  
Vol 507 ◽  
Author(s):  
J.P. Conde ◽  
H. Silva ◽  
V. Chu
Keyword(s):  
Thin Film ◽  
Active Layer ◽  
Thin Film Transistors ◽  
Silicon Layer ◽  
Active Layer Thickness ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
High Hydrogen ◽  
Hydrogen Dilution ◽  
Active Layers

ABSTRACTBottom-gate thin film transistors (TFT) were fabricated with amorphous and microcrystalline silicon active layers deposited by hot-wire (HW) chemical vapor deposition using different levels of hydrogen dilution. As the hydrogen dilution was increased above 80%, the active layer made a transition from amorphous to microcrystalline. This transition resulted in an increase of the TFT off-current and in an increase of the TFT subthreshold slope. The TFT on- current and the TFT mobility remained at levels comparable to those of the a-Si:H HW TFTs. A comparison is made between TFTs with amorphous and microcrystalline silicon active layers prepared both by rf glow discharge and HW. HW TFTs with an active layer consisting of a thin layer deposited with high hydrogen dilution underlying a thicker amorphous silicon layer are also compared to TFTs with an active layer of the same total active layer thickness consisting only of the high hydrogen dilution film.

Defects in Microcrystalline Silicon Prepared With Hot Wire CVD

2002 ◽  
Vol 715 ◽  
Author(s):  
F. Finger ◽  
S. Klein ◽  
T. Dylla ◽  
A. L. Baia Neto ◽  
O. Vetterl ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Thin Film Solar Cells ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Grain Sizes ◽  
Preparation Conditions ◽  
Hydrogen Dilution ◽  
Process Gas

AbstractThe influence of the preparation conditions in hot wire chemical vapour deposition (HWCVD) on the electronic properties of microcrystalline silicon is investigated in view of application of the material in thin film solar cells. Poor grain boundary passivation, as a result of hydrogen etching at strong hydrogen dilution of the process gas or thermal desorption of hydrogen at high deposition temperatures, is considered a main obstacle for material optimisation. We conclude that optimum μc-Si:H solar cell material, both from HW-CVD and from plasma enhanced CVD, is not necessarily obtained with largest grain sizes and apparent highest crystalline content, but rather by a material prepared under conditions which yield a compact morphology with an effective grain boundary passivation.

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