Evaluation of Semiinsulating Annealed InP:Ta for Radiation Detectors

InP crystals were grown by the Czochralski technique. They were purified by inclusion of Ta into the growth melt and then converted to the semiinsulating state by annealing. Various annealing regimes were examined to find the optimum material for radiation detectors. Temperature dependent Hall measurements were carried over the range from 300 to 430 K and the activation energy of the impurity responsible for the semiinsulating state was determined from the slope of a straight line plot to be 0.75 eV from the conduction band edge. This energy is different from the activation energy, 0.65 eV, of Fe²⁺ in InP which was observed for annealed InP grown with an admixture of Fe. An InP wafer selected for fabrication of prototype particle detectors was lapped and chemomechanically polished on the both sides to a final thickness of 0.25 mm. The detectors themselves were fabricated by deposition of circular metal electrodes of 1 mm diameter on both sides of the wafer, using vacuum evaporation of Ni/Ge/Au. The performance of these particle detectors was characterised by pulse-height spectra obtained with alpha particles emitted from ²⁴¹Am. The maximum of the spectral line measured at 300 K corresponded to an 85% charge collection efficiency when 100 V voltage was applied