Optical Absorption by Excitons in Amorphous Selenium

Abstract

Evidence is presented in support of a postulate proposed by Hartke and Regensburger in 1965, that the absorption edge in amorphous selenium is dominated at room temperature by an exciton band. Measurements of the temperature shift of the absorption edge show that the temperature shift decreases rapidly as the absorption increases, reaching negligible values well before the maximum absorption is reached. Photoconductive and nonphotoconductive components of the absorption are resolved on the basis of quantum efficiency. The nonphotoconductive or exciton component of absorption is related to vibrational frequencies of the short-range atomic order.