LIGHT INDUCED MODULATION OF ABSORPTION (LIMA) IN COPPER-DOPED SINGLE CRYSTALS CdS PLATELETS:Part II - Theoretical

摘要

Copper-doped CdS single crystal platelets were excited with chopped laser light and, by using a weak light probe in the extrinsic range, modulated optical transmission was detected. Broadband modulated transmission was detected from 5200A to 10,000A with very little structure. The modulated transmission appeared in two ways. When the phases of the modulated transmission and chopped laser light were nearly equal, enhanced transmission was observed. This was detected with a weak light probe from 5200A to 5600A and corresponded to the in-phase filling of electrons into electron traps due to chopped laser excitation. By filling electron traps, electron transitions from the valence band to these levels are made less probable and transmission is increased throughout the crystal. An apparent discrepancy was observed between the magnitude of our optical transmission measurements and predictions of a simple theoretical model constructed. This can be resolved by assuming that a deeper trap contributes to the modulation.