We have succeeded to grow chemical-vapor-deposited diamond films at reasonably high growth rates using high microwave power of 3.8 kW and high methane concentration ratios (CH4/H2) of ≥4.0%. Growth rates of ≥2 μm/h have been attained for (100) homoepitaxial growth by utilizing high-density microwave plasma. These homoepitaxial films thus grown had flat surfaces with a small number of hillocks but no non-epitaxial crystallites over the whole area of 3 × 3 mm2 high-pressure/high-temperature-synthesized Ib diamond substrates. These films yielded strong free-exciton-related emissions in their cathodoluminescence (CL) spectra taken at room temperature, indicating substantially high crystalline quality. Thus, the process technique using high-power microwave plasma for high-quality diamond growth is a remarkable advance in comparison with a very low rate growth of <0.1 μm/h using low microwave power system. Visible CL emissions originating from the Ib diamond substrate used was strongly observed from the overgrown thin homoepitaxial films with high quality. Both dependences of the CL intensities and CLimages on the ovelayer thickness suggest large diffusion lengths (of several μm) for free carriers in the films, reflecting their high crystalline quality. The possible origin of the high-quality diamond growth process attained is discussed in relation to the high-power microwave plasma employed.
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Teraji et al. (2003) studied this question.