Picosecond Dynamics of Optically Induced Absorption in the Band Gap ofAs2S3

Time-resolved absorption measurements are reported which imply an upper limit of 1 psec on the localization time for optically excited carriers in amorphous and crystalline ${\mathrm{As}}_2$ ${\mathrm{S}}_3$. These measurements also imply a short recombination time in crystalline ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ (${\tau }_c\approx 14$ psec), but a long recombination time in amorphous ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ (${\tau }_a\gg 300$ psec). This transient induced absorption does not decrease as sharply with increasing wavelength as a previously reported metastable absorption.