Effect of Fast-Neutron Irradiation on Optical Attenuation in Compound Semiconductors

Recently a model was proposed to account for anomalous infrared attenuation noted experimentally for fast-neutron-irradiated, compound semiconductors. The model represents neutron damage by localized phase transitions to a high-pressure metallic-like state. It is shown that this model not only accounts for the anomalous, continuous optical attenuation at photon energies less than the band gap, but also can explain the absorption edge fuzziness noted for neutron-irradiated GaAs. The optical attenuation produced by embedded metallic zones at frequencies above the absorption edge is derived, and it is shown that the metallic resonance absorption band is altered from the usual Lorentzian shape. It is shown that in GaAs irradiated with fast neutrons at sufficiently high doses the resonant absorption by the metallic phase can dominate the host semiconductor absorption.