Picosecond Relaxation of Optically Induced Absorption in Amorphous Semiconductors

Abstract

Picosecond relaxation of optically induced absorption in $a$-Si, $a$-Si:H, and ${\mathrm{As}}_{2}{\mathrm{S}}_{3\ensuremath{-}x}{\mathrm{Se}}_{x}$ ($0.25<~x<~0.75$) was studied with a passively mode-locked cw dye laser. In silicon, the results can be described in terms of trapping by defects. The fast recovery of absorption in chalcogenides indicates that recombination of highly localized excitons is the dominant mechanism in the decay of carriers excited at the Urbach edge.