Structural characterisation of ionising-radiation detectors based on CVD diamond films

A detailed structural characterisation of synthetic diamond films, previously investigated as UV photodetectors, has been carried out by SEM, X-ray diffraction, catholuminescence (CL), micro-Raman spectroscopy and micro-photoluminescence. The films were deposited by microwave plasma enhanced chemical vapour deposition using a CH4-CO2 gas mixture. The effect of a systematic change of the methane concentration on film morphology, preferential orientation and crystal quality has been investigated at two different substrate temperatures, 750°C and 850°C. A strong decrease of both band-A CL and width of the diamond Raman line at 1332 cm-1 has been observed, at lower substrate temperature, going towards (1 0 0) texturing, consistent with the attribution of band-A luminescence to the presence of structural defects such as dislocations. A strong correlation between methane-induced texturing and UV detector performance has been evidenced: poorly oriented films exhibit a better UV photoresponse than highly textured films. Raman and luminescence measurements suggest that the limiting factor for the detector performance is related, rather than to structural defects to centres of different nature, whose density strongly depends on the sample preferential orientation.