Study of sub-bandgap photo-induced absorption in a-Si:H using excitation spectroscopy in a waveguide configuration

The photo-induced absorption of λ = 1.3 μm light in an a-Si based waveguide is studied by means of excitation spectroscopy. At very high levels of the pump intensity the probe beam absorption tends to saturate. This phenomenon is related to high order recombination mechanisms. It is shown that the interface absorption makes a significant contribution to the absorption process. The experiments reveal the existence of localized interface states with energies which lie close to the mobility edges of a-Si and which are slightly different for the two interfaces.