Characterisation of vertical gradient freeze semi-insulating InP for use as a nuclear radiation detector

The performance of a nuclear radiation detector fabricated from Vertical Gradient Freeze (VGF) semi-insulating Fe-doped InP was investigated. Pulse height spectra were acquired when the detector was irradiated with alpha particles from 241Am, as a function of temperature and detector bias voltage. The spectroscopic performance of the detector was limited at room temperature due to the presence of a high leakage current. At a bias of −150 V, a room temperature leakage current density of 2.4×10−6 A/mm2 was observed which reduced to 7.1×10−8 A/mm2 at a temperature of −21°C. By biasing the irradiated detector contact at either a negative or positive potential, the charge collection efficiency (CCE) was measured separately for pulses produced predominantly by electron transport and for pulses produced predominantly by hole transport, respectively. At −21°C a maximum CCE of 72% was obtained for the electron signal and 44% for the hole signal. As a function of bias the CCE of the electrons remained constant in the temperature range −21°C to +19°C, whilst that of the holes exhibited a significant variation. By comparison with the Hecht relationship estimates of the carrier mobility–lifetime (μτ) products are deduced, which are similar for both holes and electrons and in the range 5×10−7–8×10−7 cm2/V. A reduction in μτ is observed at lower temperature for holes, whereas the value for electrons remains constant over the temperature range studied.