Optical properties of electron- and neutron-irradiated gallium arsenide

Results of infrared absorption and photoconductivity measurements in electron- and neutron-irradiated GaAs are presented. The structureless absorption at 300 °K in electron-irradiated samples can be expressed by α(E) = A exp (B E2), where E is the photon energy. A similar variation in absorption is observed in low fluence neutron-irradiated samples (< 6 × 1016 neutrons/cm2). This variation in absorption is attributed to the presence of a tail in the density of states at the band edges. At fluences >6 × 1016 neutrons/cm2, the absorption coefficient is found to vary linearly as the square of the photon energy. This behaviour can be explained on the basis of the presence of disordered regions containing metallic precipitates. A broad absorption band at 1.0 eV is observed in electron-irradiated samples at low temperatures while weak bands are observable at 0.47 and 0.25 eV at room temperature in neutron-irradiated GaAs. A model to explain the observed absorption data is proposed.