Comparison of vertical gradient freeze bulk GaAs and custom grown vertical zone melt bulk GaAs as radiation spectrometers

Custom grown vertical zone melt (VZM) ingots of GaAs have been zone refined and zone leveled. The crystallinity, impurity concentrations, defect concentrations, and electrical properties of the ingots have been studied. Radiation detectors fabricated from the ingots have been compared to radiation detectors fabricated from commercially available vertical gradient freeze (VGF) material. Preliminary results suggest that electrical homogeneity may be a major factor in determining the performance of GaAs gamma ray detectors. Deep level EL2 concentrations were reduced in the VZM material, however gamma ray detectors fabricated from the material exhibited inferior resolution. Commercial semi-insulating bulk VGF GaAs material demonstrated much better resolution than the VZM detectors, giving best energy resolutions of 7.8% FWHM for 122 keV gamma rays and 5% FWHM for 356 keV gamma rays.