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.