Neutron-Induced Metallic Spike Zones in GaAs

The metallic spike model for neutron damage has been shown to account for the observed anomalous infrared absorption in GaAs. In this paper, the electrical properties of semiconductors containing metallic spikes are explored. The metallic zones are shown to act as deep potential wells which trap carriers from the host semiconductor energy bands. The component of mobility associated with carrier scattering from the depletion region surrounding charged spikes is estimated as a function of temperature, including the temperature dependence of the trapped charge. Hall measurement data taken before and after neutron irradiation of n-type GaAs are compared with theory and good agreement is obtained. It is proposed that the high field trapping and slow release of electrons observed in neutronirradiated Gunn diodes is associated with the presence of metallic spikes. Hot electrons in high field domains penetrate the electrostatic barrier and are trapped within the spikes. When the low field condition is restored, excess electrons return to the host semiconductor matrix. The rate of escape of excess electrons is estimated from considerations of the processes of emission over and tunneling through the electrostatic barrier. Measurements of the temperature - dependent decay rates of the excess charge are obtained from neutron-irradiated Gunn diodes. Two decay rates were obtained at each temperature. The shorter decay time shows a temperature dependence consistent with a quantum tunneling mechanism. The longer decay time shows a stronger temperature dependence which is in qualitative agreement with emission of electrons over the barrier.