Experimental study on synthesis of single crystal diamond by hot filament chemical vapor deposition method

The deposition area of the hot filament chemical vapor deposition (HFCVD) method can reach 12 inches, which has the potential to produce larger-sized single crystal diamonds. In this study, single crystal diamond with a size of 3 mm × 3 mm × 1 mm and (100) orientation was used as the substrate. Homoepitaxial growth was carried out using the HFCVD method with methane and hydrogen as precursors, and a small amount of nitrogen gas. The results show that under the conditions of a filament temperature of 2200 °C, a carbon source concentration of 4%, and a chamber pressure of 4 kPa, single crystal diamond grows at a rate of 3.41 μm/h. The surface of the diamond exhibits no defects such as polycrystals, cracks, or holes. The full width half maximum (FWHM) of the epitaxial layer’s X-ray diffraction spectrum at the (400) peak is 0.11°, which is lower than that of the substrate at 0.16°, indicating that the crystal quality of the epitaxial layer is higher than that of the substrate. The introduction of nitrogen can increase the growth rate of single crystal diamond, although it reduces the crystal quality of the epitaxial layer. A higher nitrogen concentration can also shift the growth mode of single crystal diamond change to island growth.