Structural characterization and transport properties of diamond films prepared by dc plasma glow discharge CVD

We present in this paper results of characterization of CVD diamond films prepared with a de plasma glow discharge method at different methane concentrations and substrate temperatures. SEM analysis combined with x-ray diffraction measurements and micro-Raman spectroscopy have been used to determine the morphology and texture of three diamond samples prepared at a constant methane to hydrogen ratio (3.8 vol%). The change of the morphology with substrate temperature in the range 950-1100 degrees C is consistent with reported measurements performed on diamonds prepared by microwave-enhanced CVD, This confirms the assumption that the structural properties of CVD diamond are tunable with the deposition parameters and do not depend on the particular method of plasma activation. Micro-Raman spectroscopy combined with I-V measurements depicts the transport process as conduction along grain boundaries due to low-resistivity graphite-like phases. The resistivity is found to increase with decreasing growth rate up to a value of 10(13) Ohm cm for a deposition rate of 10-20 mu m/h. Thus, the rate of growth is regarded as a quality parameter, which takes into account the combined effects of methane concentration and substrate temperature at constant power density. The leakage currents for the sample with higher resistivities are still dominated by the contribution of the nondiamond carbon phases at room temperature and by nitrogen impurities al higher temperatures.