CVD diamond for radiation detection devices

CVD diamond is a remarkable material for the fabrication of radiation detectors. Radiation hardness, chemical resistance and high temperature operation capabilities of diamond explain its use in the fabrication of devices operating in hostile environments such as that encountered in the nuclear industry and in high energy physics. For this purpose, we have investigated the growth of high quality chemically vapour deposited (CVD) polycrystalline diamond as well as specific material and device processing. CVD diamond films were grown using the microwave plasma enhanced technique. Deposition processes were optimised according to the application requirements. This includes the synthesis of films with high sensitivity, with weak optical absorption in the UV-VIS domain or with short carrier lifetime. One inherent problem with diamond is the presence of defect levels altering the detection characteristics: these may be the cause of an observed instability of the device responses. We have found, however, that it was possible to moderate these trends through the fine-tuning of the growth conditions and of the device preparation steps. Films with thicknesses ranging from 5 to 500 μm have been used for detector fabrication. The role of post-growth treatments and the contact formation procedure was also extensively studied, leading to significant improvements of the detector characteristics. We present recent developments studied at CEA for material optimisation towards its use for specific applications, including radiation hard counters; X-ray intensity, shape and beam position monitors; solar blind photo-detectors, and high dose rate gamma-meters.