Plasma deposition of amorphous SiC:H,F alloys from SiF4‐CH4‐H2 mixtures under modulated conditions (original) (raw)
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Journal of Applied Physics, 1997
a-SiC:H films with energy gap in the range 2.00-2.65 eV have been grown by plasma enhanced chemical vapor deposition in undiluted and H 2 diluted SiH 4 ϩCH 4 gas mixtures, by making use of optimized deposition conditions. A complete picture of structural, compositional, optoelectronic, and defective properties for high quality films has been drawn for the first time. We show that the addition of H 2 to the gas mixture leads to a different chemical composition of the deposited films; in particular, carbon incorporation is enhanced and a carbon fraction in the solid matrix up to C/͑CϩSi͒Ϸ0.45 can be obtained. These films have a higher mass density, a reduced microvoid and carbon cluster concentration, a better structural connectivity, and improved optoelectronic properties. For samples with optical gap below 2.4 eV, the reduced defect concentration of H 2 diluted films results in an increase of the photoconductivity gain and the steady-state () ss values up to two orders of magnitude.
Growth chemistry of SiC alloys from SiF4–CH4 plasmas
Applied Surface Science, 2001
The deposition of SiC:H,F films from SiF 4-CH 4 plasmas is investigated: the emphasis is on the role of H and F atoms in determining the carbon and silicon etching processes. It is found that the H 2 addition to the SiF 4-CH 4-He mixture affects the relative amounts of the H and F atoms in the plasma phase. The H/F ratio controls the deposition rate, the composition and the structure of silicon carbon alloys.
Evidence for microstructure in glow discharge hydrogenated amorphous Si-C alloys
Solar Cells, 1987
We examined the IR-active 2000 -2100 cm -1 absorption peak and the photoconductivity of hydrogenated amorphous Si-C (a-SiC:H) alloys deposited from a glow discharge. We find that the existence of a frequencyshifted mode centered at 2070 cm 1 and the significant drop in photoconductivity observed to occur in a-SiC:H films with very small (greater than 1.5 at.%) carbon content can be satisfactorily explained by the presence of a microvoid structure. We also suggest that the deterioration in a-SiC:H electronic properties might be due almost entirely to microstructural effects, and therefore, if this microstructure could be eliminated, a high band gap a-SiC:H material with a photoresponse as good as that of glow discharge a-Si:H would be possible.
Properties of a-SiC:H films deposited in high power regime
Thin Solid Films, 2003
The aim of the present paper is the study of the RF power effects on the properties of hydrogenated amorphous silicon-carbon (a-SiC:H) films, deposited in high power regime in a conventional plasma enhanced chemical vapor deposition system by using silane-methane gas mixtures highly diluted in hydrogen. Varying the RF power chemically ordered a-SiC:H alloys can be grown controlling the carbon content, CywCqSix, and consequently the energy gap from 0.20 to 0.57 and 2.17 to 3.23 eV, respectively. C-rich films show defect density lower than 2=10 cm and photoluminescence (PL) at room temperature. The PL peak 17 y3 position of the spectra shifts from 1.70 to 2.54 eV as the carbon content increases from 0.3 to 0.57. ᮊ
Optical constants of silicon films deposited by the r.f. glow discharge of SiCl4
Thin Solid Films, 1981
The absorption coefficients and the refractive indices of silicon films deposited by using a glow discharge in an SiC14-H 2 mixture were measured. Specimens were deposited with one deposition parameter being varied and the others kept constant. The dependence of the optical constants on the various deposition parameters was determined. The optical gap was ,calculated by applying Tauc's analysis to the absorption data. The results are interpreted in terms of the hydrogen and chlorine contents and of the morphological changes in the silicon network.
Photoluminescent, wide-bandgap a-SiC:H alloy films deposited by Cat-CVD using acetylene
Thin Solid Films, 2001
Hydrogenated amorphous siliconycarbon films (a-Si-C:H) are deposited from a silane and acetylene gas mixture by the catalytic chemical vapour deposition (Cat-CVD) technique. It is observed that under certain conditions of total gas pressure and filament temperature (T ), the optical bandgap varies non-linearly with the acetylene to silane (C H ySiH ) ratio, having a maximum F 2 2 4 value of 3.6 eV for a C H ySiH ratio G0.8. However, the deposition rate drastically reduces with an increase in acetylene 2 2 4 fraction. FTIR spectra indicate that the total hydrogen content is lower compared to samples deposited by PECVD using similar gas mixtures, with hydrogen being preferentially attached to carbon rather than silicon atoms. The photoluminescence (PL) spectra of these films show PL in the visible spectral region at room temperature. The films with larger bandgap ()2.5 eV) exhibit PL at room temperature, with the emission having peak energy in the range 2.0-2.3 eV.
Light induced defects in amorphous silicon-carbon alloys a-SiC:H
Optical Materials, 1996
Silicon-carbon alloys were prepared using a UHV PECVD system by the mixture of CH 4 + Sill 4 with and without hydrogen dilution. The CH 4 fraction in the plasma was varied between 40 and 95%. The energy gap of our samples varies between 1.8 and 2.5 eV. The effect of degradation induced by light exposure for several hours was studied using Photothermal Deflexion Spectroscopy (PDS). The experimental data are consistent with a bond breaking model, by conversion of tail weak bonds into dangling bonds. The data show more stability in the optoelectronic properties of diluted samples.
Journal of Applied Physics, 2004
The use of very high frequency (VHF) plasma enhanced chemical vapor deposition in a capacitive discharge is investigated to fabricate hydrogenated amorphous silicon carbon alloys, using silane and methane as silicon and carbon precursors, respectively, and hydrogen dilution of the gas mixture. The properties of samples differ significantly from that is normally observed for rf deposition. A wide band-gap material is obtained, with a carbon ratio ranging from 0.2 to 0.63. An energy gap up to 3.4 eV is measured, indicating a large sp 3 content. The most interesting properties are observed using 90% hydrogen dilution and 350°C as substrate temperature. In this case, a Siu C bond concentration up to 6 ϫ 10 22 cm −3 was measured for stoichiometric samples, associated to a highly crosslinked structure and no detectable Siu CH 3 bending signal. The role of hydrogen in determining the optical properties of the film is established and is shown to affect mainly the valence electron concentration. Based on the free energy model, hydrogen bonding is observed to lie in between a random and chemically ordered configuration. The results are obtained at a deposition rate much larger than both rf and electron cyclotron resonance deposition, and are associated to a limited gas consumption, both aspects being advantageous for practical applications. The large Siu C bond concentration, associated to a limited silicon and carbon hydrogenation, makes the VHF deposited a-SiC : H a good starting material for subsequent crystallization.
Japanese Journal of Applied Physics, 1998
Hydrogenated amorphous silicon carbide (a-SiC:H) films were deposited by using a combination of radio frequency plasma enhanced chemical vapour deposition (RF-PECVD) and heated filament techniques with the objective of improving the quality of the films due to the possible beneficial effect of the latter technique. The atomic hydrogen produced via electron (emitted from the filament) impact dissociation of the process gases plays a significant role in improving the properties of the film such as the structure and bonding configuration. The electrons emitted from the hot filament also help in dissociation of methane molecules into different types of radicals. From the characterization of the films thus produced it is seen that by the combination of the two methods of deposition under optimised condition carbon is incorporated more as a Si–C bond which is structurally better. These results in better opto-electronic properties at high band gap of a-SiC:H which also shows lower light in...
Journal of Non-crystalline Solids, 2006
We have studied the photoluminescence (PL) of a nanostructured material consisting of silicon nanocrystals embedded in an amorphous matrix that we call polymorphous silicon carbon (pm-Si1−xCx:H). The presence of silicon nanocrystals in the a-Si1−xCx:H matrix is confirmed by high resolution transmission electron microscopy (HRTEM) as well as by their PL emission features, in particular a strong room temperature emission and a broad spectrum, which are characteristic of silicon nanocrystals. Moreover, the PL intensity was found to be closely related with the number of nanocrystals in the film, which depends on the deposition conditions, in particular the RF power. Possible ways to enhance the PL efficiency and a model of the recombination routes are discussed.