In the last ten years, several compound semiconductors have been studied for realising X-ray detectors. The research activity is driven by three main guidelines: improving the detection efficiency by taking into account high Z materials, approaching room temperature operation with wide bandgap semiconductors, searching for materials resistant to radiation damage.
Gallium Arsenide has been intensively studied and interesting results have been recently reached demonstrating charge collection efficiencies of almost 100% and equivalent noise charge of 24 electrons r.m.s. (240 eV FWHM for X-rays) at room temperature and 16 electrons r.m.s. (160 eV FWHM) at -30C with pixel detectors. A detailed analysis of the noise sources in these detectors, including trapping phenomena, will be presented in order to highlight the margin of further improvements and the limiting factors of these detectors. In particular a study on the origin of the leakage current in Schottky and pn junction on GaAs will be presented. The relative importance of the front-end electronics for the optimisation of the resolution performance will be addressed as well.
Another material which is giving interesting results in the last few years is Silicon Carbide. SiC radiation detectors has been recently fabricated showing extremely low leakage current densities, down to few pA/cm² even above room temperature. SiC pixel detectors with 17 electrons r.m.s. (300 eV FWHM) at 27C and capable to operate at high temperature with adequate resolution have been realised. Equivalent noise charge of 44 electrons r.m.s. (797 eV FWHM) has been measured with the detector/front-end at 100C The present limits and the perspectives for further improvements of SiC detectors and related front-end electronics will be addressed.

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1. Silicon carbide for room and high temperature X-ray detectors