Heteroepitaxial growth of high-quality (111)-oriented single-crystal diamond on Ir(111)/Al2O3(11-20) via bias-enhanced nucleation

Most heteroepitaxial diamond growth has been carried out on (100)-oriented substrates, with comparatively fewer investigations exploring the (111) orientation. Nevertheless, (111)-oriented single-crystal diamond presents specific advantages, particularly regarding higher doping efficiency and the enhanced formation of nitrogen-vacancy (NV) centers. In this study, composite substrates of Ir(111)/Al₂O₃(11-20) and AlN(0001)/Si(111) were fabricated. A bias-enhanced nucleation (BEN) process was employed, and under a bias voltage of 230 V applied for 30 minutes, diamond nucleation densities exceeding 1010 cm⁻² were achieved on both substrates. Subsequent 10-hour microwave plasma chemical vapor deposition (MPCVD) resulted in the formation of nanocrystalline polycrystalline diamond films on the AlN(0001)/Si(111) substrate, whereas single-crystal diamond with (111) orientation was successfully epitaxially grown on the Ir(111)/Al₂O₃(11-20) substrate. The full width at half maximum (FWHM) of the X-ray rocking curve for the (111) diamond plane was measured to be 0.94°, indicating high crystalline quality.