Semi-insulating bulk GaAs thermal neutron imaging arrays

Prototype thermal neutron imaging arrays have been fabricated from semi-insulating (SI) bulk GaAs. The arrays are 1 mm square Schottky diodes arranged in a 5×5 matrix. GaAs Schottky barrier radiation detectors are relatively radiation hard and can withstand higher neutron and gamma ray exposure fields than MOS-based Si diode imaging arrays. The devices use ¹⁰B to convert incident thermal neutrons to energetic Li ions and alpha particles. The truncated field effect observed with SI bulk GaAs detectors produces high and low field regions in the device. Electron-hole pairs produced in the active (or high field) region of the device contribute to the observed induced charge, whereas electron-hole pairs produced in the low field region contribute very little to the induced charge. The effect is manipulated to reduce the background gamma ray interaction rate in the devices. Preliminary results show no indication of device degradation after exposure to a total thermal neutron fluence of 1.73×10¹³ n/cm² . Images have been formed of 1, 1.5, and 2 mm holes and crosses from 2 mm thick Cd templates