INFLUENCE OF HYDROGEN DILUTION ON THE OPTOELECTRONIC PROPERTIES OF GLOW-DISCHARGE AMORPHOUS-SILICON CARBON ALLOYS

This work reports the influence of diluting with hydrogen the gaseous mixture of methane and silane on the electrical and optical properties of silicon-carbon alloys deposited by glow discharge. Impressively high secondary photoconductivities, low density of gap defects states and Urbach energy parameter were found in materials prepared in suitable hydrogen dilution conditions. Experiments on temperature dependence of dark and under white light illumination conductivity are also reported and interpreted. Depending on the dilution and substrate temperature, the Fermi level shift toward the conduction band, suggesting a combined effect of low density of defects and sensitization as the causes of the high photoconductivities. IR studies show that appropriate hydrogen dilution and substrate temperature prevent the silicon atoms from forming high order hydrides. Consequently, a more compact structure with better electronic properties is obtained.