Characteristics of near-band-edge absorption processes in bulk GaAs

Some important characteristics of near band-edge absorption and photo-current were investigated in both n-type and semi-insulating GaAs. A remarkable absorption process peaking at 1.499 meV (at 10 K) with full-width at half-maximum of about 4 meV was extracted from the absorption spectra of both materials. Parellel photo-current and absorption spectra extends from 1.495 eV towards the band-edge at sample temperature of 10 K. As the sample temperature is increased, this extension shifts towards the band-edge and disappears at just above 100 K. Extrapolation of Eg–EmaxEg–Emax versus temperature plots show that this absorption level becomes degenerate with the conduction band at sample temperature just above 200 K. We propose that all the absorption is associated with ionization and that a model of photo-ionization of a deep level near the conduction band by an electron (or electrons) from the valance band may describe the observed phenomena.