Measurement and modeling of the x-ray spectral response of bulk GaAs detectors

摘要

In light of recent developments in hard x-ray focusing, work has been carried out at the University of Leicester, to investigate the use of high-Z materials (principally GaAs) for detecting x-rays in the 10 to 100 keV regime. The x-ray astronomy group at Leicester has been involved with developing the detectors and optics for several instruments including the Rosat wide field camera, JET-X an XMM, but both the grazing incidence optics, and the quantum efficiency of more conventional detectors, e.g. silicon CCDs, have limited the energy response to less than 10 keV. Ge, CdTe, HgI and GaAs all offer higher quantum efficiency than silicon and are being investigated as a possible means to extending the energy response of future telescopes, aimed at studying non-thermal processes beyond the iron lines. Detectors have been fabricated using bulk and epitaxially grown GaAs and tested at a range of temperatures between minus 130 degrees Celsius and room temperature. The behavior of bulk GaAs detectors is dominated by carrier trapping leading to imperfect charge collection efficiency (CCE) and traditionally poor spectral resolution. Noise-dominated spectra with 2 keV full width at half maximum (FWHM) are presented. The results of a Monte Carlo simulation of spectral performance are compared to the measured spectra. The modeling enables one to characterize the traps in terms of cross section density products and trap release times.