Gamma-Radiation Damage in Epitaxial Gallium Arsenide

Abstract

Electrical and photoluminescence measurements were carried out on liquid epitaxial GaAs single crystals after irradiation at room temperature by 1.25‐MeV ⁶⁰Co γ rays. Following each of a series of irradiations, Hall measurements were made on both n‐ and p‐type crystals as a function of temperature between 77 and 300°K. The n‐type crystals exhibited energy levels 0.13, 0.16, and 0.30 eV below the conduction band minimum after irradiation. The 0.13‐ and 0.16‐eV levels were introduced during irradiation at roughly one‐half the rate at which compensating deep acceptors were introduced. The p‐type crystals showed energy levels 0.059 and 0.10 eV above the valence band maximum. Before irradiation, these p‐type crystals had energy levels in the lower 0.20 eV level of the band gap. It is, therefore, not possible to determine whether the 0.059 and 0.10 eV were produced by irradiation or were merely uncovered as the free‐hole density was reduced by radiation‐induced deep donors. The carrier removal rate at 77°K was 0.012 cm⁻¹ for p‐type crystals. Photoluminescence measurements on irradiated material revealed additional energy levels near the center of the band gap.