Quenching effects induced by additional below-bandgap illumination in undoped semi-insulating material were investigated by using optical admittance spectroscopy and photo-current spectroscopy as well as optically excited, thermally stimulated currents. In optical admittance spectroscopy and photo-current, a decrease in defect-related signals due to the quenching light was observed. The thermal quenching of the defect band between 2.7 and 3.3eV exhibited good agreement with thermal emissions as measured by thermally stimulated currents, indicating that the same defects caused the optical transitions in optical admittance spectroscopy and photo-current spectroscopy and the thermal transitions in thermally stimulated currents. The thermal emission at 250 to 300K, which was responsible for the thermal quenching of the blue band in optical admittance spectroscopy, also exhibited an optical quenching under below-bandgap excitation.

Deep-Defect Induced Quenching Effects in Semi-Insulating GaN Layers Detected by Photo-Electrical Spectroscopic Techniques. H.Witte, A.Krtschil, M.Lisker, E.Schrenk, J.Christen, A.Krost, B.Kuhn, F.Scholz: Applied Physics Letters, 2003, 82[23], 4083-5