LARGE PHOTOINDUCED PERSISTENT OPTICAL-ABSORPTION IN SELENIUM DOPED ALSB

Low-temperature, T<90 K, illumination transfers transparent, single crystals of AlSb doped with Se to a metastable state characterized by a high optical absorption approaching 200 cm(-1) The enhanced absorption spectrum extends from 0.1 to 1.5 eV and consists of a double band structure with peaks at 0.2 and 0.5 eV. It is induced by photons with a threshold energy of about 1 eV. It is persistent, i.e., it shows no measurable decay after switching off the excitation. The low absorption state is thermally recovered at 100 K. The persistent absorption is a manifestation of a DX-type bi-stability of the Se donor. The 0.2 and 0.5 bands are, respectively, due to the photoionization of electrons from the metastable hydrogenic donor level to X(1) and X(3) conduction band minima. A large binding energy of the Se donor is essential for the observation of persistent absorption and a lack of any free-electron related effects. (C) 1995 American Institute of Physics.