Optoelectronic and structural properties of amorphous silicon-carbon alloys deposited by low-power electron-cyclotron resonance plasma-enhanced chemical-vapor deposition

The optoelectronic and structural properties of hydrogenated amorphous sili con-carbon alloys (a-SiC:H) are studied over the entire compositional range of carbon content. The films are prepared using low-power electron-cyclotr on resonance (ECR) plasma-enhanced chemical vapor deposition. The carbon co ntent was varied by using different methane (or ethylene-)-to-silane gas ph ase ratios and by introducing the methane (or ethylene) either remotely int o the plasma stream or directly through the ECR source, together with the e xcitation gas (hydrogen). Regardless of the deposition conditions and sourc e 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 defec t density from photothermal deflection spectroscopy, the ESR spin density, the steady state and the transient photoluminescence, the dark and photocon ductivity, 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 absorp tion coefficient is equal to 10(4) cm(-1)). Silicon-rich and carbon-rich re gions with very different properties, corresponding approximately to carbon fractions below and above 0.5, respectively, can be distinguished. The pro perties of the ECR a-SiC:H alloys are compared with those of alloys deposit ed by rf glow discharge. (C) 1999 American Institute of Physics. [S0021-897 9(99)00606-4].