Enhancement of photoconductivity in r.f. glow-discharge-deposited a-SiC: H films doped with nitrogen

Abstract

Nitrogen-doped amorphous hydrogenated silicon-carbon alloy (a-SiC: N: H) films have been prepared by introducing nitrogen during the radio frequency (r.f.) glow-discharge decomposition of methane-silane-helium mixtures. The effects of nitrogen on the structural, optical, electrical and optoelectronic properties of the films deposited at various methane-silane flow rates have been investigated. It is found that nitrogen doping enhances the photoconductivity of the films, while the optical band-gap remains unchanged. The incorporation of nitrogen atoms leads to a lower hopping-assisted contribution to the dark d.c. conductivity at low temperatures and increases the conductivity in the thermally activated conduction regimes. Activation energies of the dark conductivity and the photoconductivity are lower in the nitrogen-doped films. These results indicate that nitrogen in the films relaxes the structural disorder and/or decreases the density of defects.