Comparative study of band-A cathodoluminescence and Raman spectroscopy in CVD diamond films

A set of diamond films was grown by microwave plasma enhanced chemical vapour deposition using a CO2-CH4 gas mixture. Film morphology, preferential orientation and crystal quality were systematically changed by varying the CH4 concentration and substrate temperature in the ranges 47-52% and 750-850 °C, respectively. The resulting films were characterised by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and cathodoluminescence (CL). The crystalline quality of the films, as assessed by Raman spectroscopy, increases at lower substrate temperatures (Ts=750 °C) and when moving from (110) towards (100) texturing. Independently of the substrate temperature, a strong decrease of the band-A cathodoluminescence at 435 nm is found as the film preferential orientation goes from (110) to (100). A clear correlation between the width of the diamond Raman line and the band-A emission is observed, giving insight into the nature of this band. In particular, this result is consistent with the attribution of band-A CL to the presence of dislocations.