TRANSPORT AND PHOTOLUMINESCENCE OF HYDROGENATED AMORPHOUS SILICON-CARBON ALLOYS

The optoelectronic properties of hydrogenated amorphous silicon-carbon alloys (a-SiC:H) are studied over the entire compositional range of carbon content. The films are prepared using radio-frequency glow discharge and optimization was made with respect to deposition power and pressure, hydrogen dilution, and methane (or ethylene) -to-silane gas phase ratio. 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 Urbach tail energy E(u) and the B factor of the Tauc plot correlate with E(04) (defined as the energy at which the absorption coefficient is equal to 10(4) cm(-1)) taken from photothermal deflection spectroscopy measurements. Up to E(04)(pds)approximate to 2.6 eV, E(u) increases monotonically from 50 up to approximate to 200 meV, while the B factor decreases from approximate to 800 down to approximate to 200 cm(-1/2)eV(-1/2). Above E(04)(pds)approximate to 2.6 eV, both E(u) and B remain approximately constant. The photoconductivity decreases exponentially with E(04)(pds) and is below 10(-10) Ohm(-1) cm(-1) for E(04)(pds)greater than or equal to 2.6 eV. Room-temperature photoluminescence is observed when E(04)(pds)greater than or equal to 2.6 eV. The photoluminescence peak position lies an average of 0.6 eV below the value of E(04)(pds) and increases linearly with decreasing value of the B factor of the Tauc plot. (C) 1995 American Institute of Physics.