The effects of varying the C acceptor concentration, and/or lowering the temperature, upon the photo-quenchability of the mid-gap donor, EL2, were studied in liquid-encapsulated Czochralski-grown semi-insulating material. The EL2 photo-quenching effect was found to be enhanced at lower temperatures, and in samples with higher C contents. A unified understanding of these phenomena was provided by assuming the existence of an acceptor level, located at 0.07 to 0.08eV above the valence band, whose charge state controlled transitions to and from the metastable state.

M.Suemitsu, H.Takahashi, Y.Sagae, N.Miyamoto: Materials Science Forum, 1995, 196-201, 1037-42