The mean energy necessary to generate an electron-hole pair in gallium arsenide by x and γ photons has been measured in the 230–320 K temperature range. The experimental apparatus consists of a Schottky junction on a high-quality epitaxial GaAs, a silicon detector that generates a reference charge signal and highly stable low-noise electronics. The resolution of the system in measuring the generation energy is better than 2 meV. An apparent value of ε=4.216 eV has been measured at 300 K, lower than previously published values of 4.35 and 4.27 eV for α particles and 4.57 eV for electrons. Charge trapping in the GaAs detector, although very weak (less than 1%), has been observed and a model, based on the Hecht theory, has been developed to derive the true value of ε=4.184±0.025 eV at 300 K. The dependence of ε on the temperature, in the 230–320 K range, has been found linear, ε=4.55−0.00122×T [eV]. The dependence of ε on the band gap has been determined ε=2.76×Eg+0.257 [eV], in good agreement with the Shockley-Klein theory. At 300 K, the found value of ε in GaAs, together with those reported for germanium and silicon, yields a linear dependence of ε on the band-gap energy ε=1.83×Eg+1.6 [eV], with a correlation coefficient of 0.9997.
The advantages of using Silicon Carbide for X-ray spectroscopy and imaging has been examined over the existing semiconductor detectors. Several SiC detectors have been manufactured and tested. They are constituted by Schottky junctions on a low doped (5x10 14 ) n-4H-SiC epitaxial layer. The diodes show extremely low reverse current densities at room temperature (£5 pA/cm 2 ) up to mean electric field of 100 kV/cm in the depleted region. These currents are two order of magnitude lower with respect to the best junctions on Silicon used for X-ray spectroscopy, so making SiC detectors extremely low noise devices. Using a pixel detector a noise of 415 eV FWHM at room temperature has been measured. Moreover for the first time an X-ray spectroscopy at high temperature has been demonstrated using a semiconductor: the SiC detector has been operated at 100°C, showing a noise of 1 keV FWHM.
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