Influence of microstructure on the Urbach edge of amorphous SiC:H and amorphous SiGe:H alloys

Abstract

Infrared measurements have been used as a means of quantifying the amount of hydrogenated amorphous silicon and amorphous silicon alloy microstructure. Using a parameter obtained from these infrared measurements, the Urbach edge of amorphous silicon (a-Si:H), amorphous silicon carbon (a-SiC:H), and amorphous silicon germanium (a-SiGe:H) obtained from photothermal deflection spectroscopy measurements fall on the same curve. This suggests that the decreasing steepness of the Urbach edge, observed to occur with increasing alloying, is due primarily to microstructural effects and not to increased structural or compositional disorder. Based upon this correlation, we suggest an explanation for the observed decrease in alloy material photoconductivity with increasing alloy content.