Room-temperature particle detectors based on purified InP single-crystals converted to semi-insulating state by annealing

InP were grown by Czochralski technique. They were purified by admixture of Ta into the growth melt and then converted to semi-insulating state by annealing. Temperature dependent Hall measurements were carried out in the range from 300 K to 430 K and the activation energy of the impurity responsible for the semi-insulating state was determined from the slope of the straight line as 0.75 eV from the conduction band edge. This energy is much different from the activation energy of Fe²⁺ in InP, 0.65 eV, which was observed in the annealed InP grown with Fe admixture. InP wafer selected for fabrication of prototype particle detectors was lapped and chemo-mechanically polished on the both sides to final thickness of 0.25 mm. The detectors were fabricated by metal deposition of circular electrodes of 1 mm diameter overlaying on both sides of the wafer, using vacuum evaporation of Ni/Ge/Au. Detection performance of particle detectors was measured at room temperature by pulse-height spectra with alpha particles emitted from ²⁴¹Am. Maximum of the spectral line corresponded to 85% of charge collection efficiency when 100 V voltage was applied