Electrical and optical properties of neutron-irradiated GaP crystals

Infrared absorption, electron paramagnetic resonance (EPR) spectra, and the electrical resistivity of semi-insulating liquid encapsulated Czochralski GaP crystals irradiated by fast neutrons with a dose of 7.6×1018 n cm−2 have been studied. The electrical resistivity decreases with irradiation from 106 Ω cm to 1.5 kΩ cm. The temperature dependence of resistivity at low temperature is fitted to exp(b/T1/4). The strong continuous optical absorption extends to 0.32 eV and its tail spreads until 0.12 eV. The EPR spectrum exhibits a broad singlet at 77 K and a doublet with five line structures at room temperature, which is attributed to antisite defects PGa. The strong infrared absorption begins to be annealed at 150 °C, and the EPR broad singlet decreases with anneals in the same temperature range. The strong infrared absorption is assumed to arise from interstitial phosphorus clusters. A discussion is given concerning the species responsible for the EPR singlet.