STUDY OF SUB-BANDGAP PHOTOINDUCED ABSORPTION IN A-SI-H USING EXCITATION SPECTROSCOPY IN A WAVE-GUIDE CONFIGURATION

The photo-induced absorption of lambda=1.3 mu m light in an a-Si:H bas ed waveguide is studied by means of excitation spectroscopy. At very h igh levels of the pump intensity the probe beam absorption tends to sa turate. This phenomenon is related to high order recombination mechani sms. It is shown that the interface absorption makes a significant con tribution to the absorption process. The experiments reveal the existe nce of localized interface states with energies which lie close to the mobility edges of a-Si:H and which are slightly different for the two interfaces.