Amorphous Silicon Carbon and Amorphous Silicon Germanium Alloy Research at SERI

The authors present results of the amorphous silicon based alloy film research performed using a capacitively-coupled RF glow-discharge system. They report and contrast the electronic and structural properties of a-SiC:H films produced using hydrogen and fluorine containing gases; and show that either graphitic-type or CH//n -type bonding, which may be present in films deposited from SiH//4 /CH//4 gas mixtures, can be eliminated using SiF//4 /CH//4 /H//2 gas mixtures, with a resultant improvement in photovoltaic response. They also combine photoconductivity and density of states data with device modeling studies to suggest that the nature of the gap states in a-SiGe:H material changes as the bandgap is lowered below 1. 5 eV, thus offering a possible explanation for the sharp drop in photoconductivity observed by many researchers.