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 c arbon content. The films are prepared using radio-frequency glow disch arge and optimization was made with respect to deposition power and pr essure, hydrogen dilution, and methane (or ethylene) -to-silane gas ph ase ratio. Regardless of the deposition conditions and source gases us ed, the optical, structural, and transport properties of the a-SiC:H a lloys followed simple universal dependencies related to changes in the density of states associated with their structural disorder. The Urba ch 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 equ al to 10(4) cm(-1)) taken from photothermal deflection spectroscopy me asurements. Up to E(04)(pds)approximate to 2.6 eV, E(u) increases mono tonically from 50 up to approximate to 200 meV, while the B factor dec reases 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 ap proximately constant. The photoconductivity decreases exponentially wi th E(04)(pds) and is below 10(-10) Ohm(-1) cm(-1) for E(04)(pds)greate r than or equal to 2.6 eV. Room-temperature photoluminescence is obser ved when E(04)(pds)greater than or equal to 2.6 eV. The photoluminesce nce peak position lies an average of 0.6 eV below the value of E(04)(p ds) and increases linearly with decreasing value of the B factor of th e Tauc plot. (C) 1995 American Institute of Physics.