Gallium Arsenide detectors for X-ray and electron (beta particle) spectroscopy

Results characterizing GaAs pþ-i-nþ mesa photodiodes with a 10 mm i layer for their spectral response under illumination of X-rays and beta particles are presented. A total of 22 devices, having diameters of 200 mm and 400 mm, were electrically characterized at room temperature. All devices showed comparable characteristics with a measured leakage current ranging from 4 nA/cm to 67 nA/cm at an internal electric field of 50 kV/cm. Their unintentionally doped i layers were found to be almost fully depleted at 0 V due to their low doping density. Fe X-ray spectra were obtained using one 200 mm diameter device and one 400 mm diameter device. The best energy resolution (FWHM at 5.9 keV) achieved was 625 eV using the 200 mm and 740 eV using the 400 mm diameter device, respectively. Noise analysis showed that the limiting factor for the energy resolution of the system was the dielectric noise; if this noise was eliminated by better design of the front end of the readout electronics, the achievable resolution would be 250 eV. Ni beta particle spectra obtained using the 200 mm diameter device showed the potential utility of these detectors for electron and beta particle detection. The development of semiconductor electron spectrometers is important particularly for space plasma physics; such devices may find use in future space missions to study the plasma environment of Jupiter and Europa and the predicted electron impact excitation of water vapor plumes from Europa hypothesized as a result of recent Hubble Space Telescope (HST) UV observations. & 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).