In Situ S-Doping of Cubic Boron Nitride Thin Films by Plasma Enhanced Chemical Vapor Deposition

In situ sulphur doping of cubic boron nitride (cBN) films was investigated by adding H2S into a plasma-enhanced chemical vapor deposition system. It was found that the nucleation of cBN was suppressed severely with a very low H2S concentration, while cBN could be grown continuously even at a H2S concentration as high as that of the boron source after its nucleation. Accordingly, S was incorporated into cBN films meanwhile keeping the cubic phase concentration as high as 95%. And a rectification ratio of approximately 10 5 was observed at room temperature for heterojunction diodes prepared by depositing S-doped cBN films on p-type silicon substrates, which suggests the possibility of an n-type-like doping. Moreover, 1500K post annealing of cBN films in H2 atmosphere was found to be able to release the residual compressive stress evidently. Thus, film adhesion strength increased markedly, and cBN films reached a thickness over 200 nm without peeling off from silicon and quartz substrates in air after 9 months.