Microstructural and electrical studies of nitrogen doped diamond thin films grown by microwave plasma CVD

We present a study of the microstructural and electrical properties of nitrogen doped diamond (NDD) thin films deposited on Si(111) by microwave plasma enhanced chemical vapor deposition (MWCVD). The conductivity of NDD thin film increases with increasing bias. In contrast, we also found the conductivity decreased with the increasing growth temperature and the increasing thickness of the diamond film after longer deposition. According to the microstructural analysis of NDD thin films by means of SEM, we found that the thicker the diamond thin film is, the bigger the grain size of the diamond grows, and the fewer interfaces the grain boundary of the NDD has, yield to a larger resistance. We propose that the nitrogen in the NDD was not doped into diamond crystallines but was located in the interlayer of the grain boundaries of the NDD.