Optimising CVD diamond properties for radiation detection applications: Growth conditions, defects, and uniformity

CVD diamond is a remarkable material for the fabrication of radiation detec tors. The radiation hardness, chemical resistance and high-temperature oper ation capabilities of diamond motivate its use for the fabrication of devic es operating in hostile environments such as those encountered in the nucle ar industry and high-energy physics. For this purpose. we have frown polycr ystalline diamond films using the microwave plasma enhanced chemical vapour deposition technique (CVD). Deposition processes were optimised according to the application requirements. This includes the synthesis of films with high sensitivity or with short carrier lifetime. Defect level influence on the detection characteristics were studied : they may be the cause of an ob served instability of the device responses. We have found, however, that it is possible to moderate these trends through the fine-tuning of the growth conditions and of the device preparation steps. Films with thicknesses ran ging from 5 to 500 mum have been used for detector fabrication. Using a mic rometer-size focused X-ray beam, we have also studied the nonuniformity of devices fabricated from polycrystalline diamond. Sensitivity maps were imag ed and correlated with the grain structure. We present here recent developm ents studied at CEA in Saclay for material optimisation for specific applic ations, including radiation hard counters, X-ray intensity, shape and beam position monitors, solar blind photodetectors, and high dose rate gamma-met ers.