Purity of epitaxial cubic BoronNitride films on (001) Diamond — A prerequisite for their doping

Phase pure cubic BoronNitride (c-BN) films were epitaxially grown on (001) Diamond substrates at 900 °C and analyzed for purity by taking X-ray Photoelectron Spectroscopy (XPS) as well as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles. No metallic impurities could be detected within the resolution limit of ToF-SIMS corresponding to some ppm. The films, however, still contain typically 0.5 at.% carbon and 1 at.% oxygen, which both can be traced back to the boron sputter target. All as-prepared c-BN films, with and without additional sputter cleaning of their surface, exhibit a p-type conductivity, which can be attributed most probably to carbon on nitrogen vacancy sites. Doping c-BN with Si during film growth turned out to be impeded at high temperatures with a strong tendency of Si to segregate towards the sample surface. While such high c-BN deposition temperatures could be demonstrated as helpful to decrease the amount of carbon and oxygen contaminants, in case of Si dopants this effect restricted the level of doping to approximately 200 ppm.