Correlation between material properties and leakage currents in CVD diamond films deposited by DC plasma glow discharge

A set of chemical vapor deposited (CVD) undoped diamond samples have been prepared by means of a DC glow discharge CVD apparatus, using the mixture of methane and hydrogen as a source gas at different methane concentrations and substrate temperature, keeping constant the power density and the gas flow. A study of the leakage current level of the samples has been carried out in order to assess the potential of the apparatus in synthesizing high quality diamonds for application in high energy physics. A particular shape of the Mo electrodes has been designed in order to achieve uniform continuous growth onto the anode. The presence of non-diamond phases has been related to the electric behavior of the samples by means of micro-Raman scattering measurements and scanning electron microscopy (SEM) analysis. At the highest growth rates, depending on methane concentration and substrate temperature, the graphite-like domains extend all over the substrate side of the samples and at the grain boundaries increasing, in the presence of an applied electric field, the leakage current values of various orders of magnitude. At lower growth rates the purity of the diamond is highly improved, resulting in a resistivity of the order of 1012–1013 Ω cm. A theoretical model has been used to estimate the order of magnitude for the sp3 to sp2 ratio in the films.