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 re fined and zone leveled. The crystallinity, impurity concentrations, de fect concentrations, and electrical properties of the ingots have been studied. Radiation detectors fabricated from the ingots have been com pared to radiation detectors fabricated from commercially available ve rtical gradient freeze (VGF) material. Preliminary results suggest tha t electrical homogeneity may be a major factor in determining the perf ormance of GaAs gamma ray detectors. Deep level EL2 concentrations wer e reduced in the VZM material, however gamma ray detectors fabricated from the material exhibited inferior resolution. Commercial semi-insul ating 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.