The optoelectronic and structural properties of hydrogenated amorphous silicon-carbon alloys ͑a-SiC:H͒ are studied over the entire compositional range of carbon content. The films are prepared using low-power electron-cyclotron resonance ͑ECR͒ plasma-enhanced chemical vapor deposition. The carbon content was varied by using different methane ͑or ethylene-͒-to-silane gas phase ratios and by introducing the methane ͑or ethylene͒ either remotely into the plasma stream or directly through the ECR source, together with the excitation gas ͑hydrogen͒. Regardless of the deposition conditions and source gases used, the optical, structural and transport properties of the a-SiC:H alloys followed simple universal dependencies related to changes in the density of states associated with their structural disorder. The deep defect density from photothermal deflection spectroscopy, the ESR spin density, the steady state and the transient photoluminescence, the dark and photoconductivity, the temperature of the hydrogen evolution peaks and the bonding from infrared spectroscopy are correlated to the Urbach tail energy, the B factor of the Tauc plot and E 04 ͑defined as the energy at which the absorption coefficient is equal to 10 4 cm Ϫ1 ͒. Silicon-rich and carbon-rich regions with very different properties, corresponding approximately to carbon fractions below and above 0.5, respectively, can be distinguished. The properties of the ECR a-SiC:H alloys are compared with those of alloys deposited by rf glow discharge.

The optical, electronic and structural properties of thin films deposited by Hot-wire chemical vapor deposition with filament temperatures, Tfil, between 1500 and 1900 °C from silane and hydrogen are studied. The substrate temperature, Tsub, was kept constant at 220 °C. Amorphous silicon films (a-Si:H) are obtained at high filament temperatures, low deposition pressures and low hydrogen-to-silane flow rate ratio (Tfil∼1900 °C, p<30 mTorr and FH2/FSiH4≤1). At these deposition conditions, high growth rates are observed (rd≥10 Ås−1) both with and without hydrogen dilution, and no silicon deposition was observed on the filaments. However, if a lower filament temperature is used (Tfil∼1500 °C) a transition from a-Si:H to microcrystalline silicon (μc-Si:H) occurs as the pressure is decreased from above 0.3 Torr to below 0.1 Torr. The highest dark conductivity and lowest activation energy, of ∼1 Scm−1 and <0.1 eV, respectively, were observed for μc-Si:H deposited at p∼50 mTorr. In this Tfil regime, μc-Si:H growth is achieved without hydrogen dilution, for substrate temperatures as low as ∼150 °C, and for very thin films (∼0.05 μm). Silicon growth on the filaments is observed. For both Tfil regimes, an amorphous to microcrystalline transition is also observed when the hydrogen dilution is increased (FH2/FSiH4≳4). A kinetic growth model is developed, which suggests that the transition from amorphous to microcrystalline can be explained by considering a balance between the concentration of atomic hydrogen and the concentration of the precursor to silicon deposition (SixHz with z≤3x) near the sample. This concentration ratio is shown to be controlled both by the deposition pressure, p, and the filament temperature, Tfil.

Hydrogenated amorphous silicon, a-Si:H, is deposited from silane and hydrogen by hot-wire chemical vapor deposition using a tungsten wire filament at a temperature Tfil=1200 °C. Film properties depend on whether the films were deposited using filaments with an accumulated deposition time lower than 90 min (‘‘new’’ filaments) or longer than 90 min (‘‘old’’ filaments). The deposition rate for films deposited with ‘‘new’’ filaments is 4 times higher than that for aged filaments. For ‘‘new’’ filaments, a monotonic increase of the growth rate, rd, with the pressure is observed, as well as a maximum of rd for FH2/FSiH4 close to unity. The optoelectronic properties are controlled by the substrate temperature Tsub, and show different dependences for ‘‘new’’ and ‘‘old’’ filaments. The Urbach band tail energy, Eu, is lower for films deposited with ‘‘new’’ filaments. A kinetic growth model for hot-wire chemical vapor deposition in the Tfil∼1200 °C regime is proposed.

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