High quality CVD diamond: a Raman scattering and photoluminescence study

High quality synthetic diamonds were grown on single-crystal silicon by mic rowave plasma enhanced chemical vapour deposition (CVD). A careful optimisa tion of both the experimental setup and the growth parameters was necessary before that the achievement of the best results was made possible. The fil ms were deposited using a CH4-H-2 gas mixture at methane concentrations var iable in the range 0.6-2.2%, while the substrate temperature was fixed at 7 50 degreesC. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study the spatial distri bution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than 2.4 cm(-1) can be easily measured at the gr owth surface, indicating that the crystalline quality of individual grains is comparable to that of the best natural diamonds. The excellent phase pur ity of the diamond microcrystals at the growth surface is witnessed by the complete absence of any non-diamond carbon feature and by a very weak lumin escence background in the 1.6-2.4 eV spectral range. A worsening of the qua lity of the diamond particles is found moving from the growth surface towar ds the film-substrate interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the exc iting laser beam is focused close to the interface. A progressive degradati on of the global quality of the films is found with increasing methane conc entration in the gas mixture, as witnessed by an increased PL background in the films grown at higher methane concentrations.