An investigation of photo-quenching properties of LEC GaAs by using optical and electrical techniques

We have performed a series of novel measurements on n-type GaAs, involving photo-quenching of Schottky capacitance and optical absorption on samples grown from melts of various stoichiometry. Decrease of Schottky capacitance by photo-quenching at temperatures below 130 K, which is normally ascribed to the photo-quenching of EL2 centres, is accompanied by optical absorption bleaching at 1 μm wavelength. After complete bleaching of both Schottky capacitance and optical absorption by EL2 centres at a measurement wavelength of 1 μm, the near-band-edge absorption extending to about 50 meV below E_g, was still present. Photo-quenching of this absorption could be observed but only at temperatures below 45 K. However, no capacitance change related to this absorption bleaching was observed. It follows that the photo-quenching of the near-band-edge absorption cannot be due to EL2 centres and that the absorption mechanisms at 1 μm and close to the band-edge are due to different defects.