Vertical-substrate epitaxial growth of single-crystal diamond by microwave plasma-assisted chemical vapor deposition

Epitaxial diamond growth by microwave plasma CVD in a CH4/H2 mixture was performed on vertically standing single crystal diamond substrates with high aspect (height-to-width) ratio. This “vertical growth” mode allows simultaneous diamond deposition on two large (1 0 0) faces of the substrate, in contrast to only one working face upon conventional horizontal arrangement of the substrate plate. A high plasma density gradient in vertical direction, the characteristic feature of the geometry used (the substrate acts as an antenna), coupled to high substrate temperature gradient (ΔT ≈ 150 °C in the particular experiment), are shown to have a strong impact on the epilayer structure, that was characterized with laser scanning microscopy, Raman and photoluminescence confocal spectroscopy mapping across ≈3 mm high specimen. The single crystal film transformation to polycrystalline, and further, to nanocrystalline layer, going from top to bottom of the substrate, is described. The vertical distributions of the growth rate, intensity of photoluminescence of NV and SiV color centers imbedded in the diamond film, are measured with high spatial resolution on growth surface and in cross-section, which are also related to the film structure variation. These findings are of importance for search of optimal growth regimes of 3D diamond mosaics and large single crystals by MPCVD.