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

A detailed structural characterisation of synthetic diamond films, previous ly investigated as UV photodetectors, has been carried out by SEM, X-ray di ffraction, catholuminescence (CL), micro-Raman spectroscopy and micro-photo luminescence. The films were deposited by microwave plasma enhanced chemica l vapour deposition using a CH4-CO2 gas mixture. The effect of a systematic change of the methane concentration on film morphology, preferential orien tation and crystal quality has been investigated,at two different substrate temperatures, 750 degrees C and 850 degrees C. A strong decrease of both b and-A CL and width of the diamond Raman line at 1332 cm(-1) has been observ ed, at lower substrate temperature, going towards (1 0 0) texturing, consis tent with the attribution of band-A luminescence to the presence of structu ral defects such as dislocations. A strong correlation between methane-indu ced texturing and UV detector performance has been evidenced: poorly orient ed films exhibit a better UV photoresponse than highly textured films. Rama n and luminescence measurements suggest that the limiting factor for the de tector performance is related, rather than to structural defects to centres of different nature, whose density strongly depends on the sample preferen tial orientation.