It was recalled that recent infra-red spectroscopic observations of local vibrational mode absorptions had revealed a number of photosensitive centers in semi-insulating material. These included an OVAs center which had modes at 730, 715 and 714/cm. There was also a suggested NH center that was related to a line at 983/cm (X1), and centers that were related to H; such as (H-O) or (H-N) bonds. The latter corresponded to a group of peaks at 2900 to 3500/cm. The photosensitivity of various local vibration centers was observed to have a similar time dependence under near-infrared illumination, and was suggested to be due to their charge-state inter-conversion. The present work concentrated upon the effect of 1.25eV illumination. It was confirmed that this photo-induced kinetic process resulted from both electron capture and hole capture. These were closely related to the photo-ionization behavior and to the metastability of the EL2 center.

C.Y.Song, B.Pajot, W.K.Ge, D.S.Jiang: Physical Review B, 1995, 52[7], 4864-9