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

AbstractResults characterizing GaAs p+-i-n+ mesa photodiodes with a 10µm i layer for their spectral response under illumination of X-rays and beta particles are presented. A total of 22 devices, having diameters of 200µm and 400µm, were electrically characterized at room temperature. All devices showed comparable characteristics with a measured leakage current ranging from 4nA/cm2 to 67nA/cm2 at an internal electric field of 50kV/cm. Their unintentionally doped i layers were found to be almost fully depleted at 0V due to their low doping density. 55Fe X-ray spectra were obtained using one 200µm diameter device and one 400µm diameter device. The best energy resolution (FWHM at 5.9keV) achieved was 625eV using the 200µm and 740eV using the 400µm 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 250eV. 63Ni beta particle spectra obtained using the 200µm 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