Dielectric property of thick freestanding diamond films by high power arcjet operating at gas recycling mode

Abstract

Dielectric property of thick freestanding diamond films prepared by high power arcjet operating at gas recycling mode was measured by the high voltage electric bridge method at low frequencies (r.f.) and the wave guide resonance method at high frequencies (microwave). It was found that, with increasing frequencies, dielectric loss of freestanding diamond films increased at low frequencies, but decreased at high frequencies, with a maximum located at approximately 3 MHz. Measurements of dielectric loss of the freestanding diamond films at a microwave frequency of 5.2 GHz showed a strong dependence on the growth parameters such as substrate temperature and methane concentration. It was found that dielectric loss decreased with increasing substrate temperature, and increased with an increasing methane concentration in the feed gases. It is suggested that dielectric loss is closely related with the quality level of freestanding diamond film samples, as demonstrated by the results from Raman and SEM observations. Non-diamond carbon in the diamond films was found responsible for the increase in dielectric loss. Nitrogen was intentionally introduced into the Ar–H 2–CH 4 gas stream for diamond deposition to investigate the effect of impurities. It was shown that nitrogen addition to the feed gases seriously deteriorated the dielectric property of the resultant diamond films. This is again in agreement with our experimental observations by Raman and SEM, in that the addition of nitrogen also seriously deteriorated the quality of the diamond film. Mechanisms for the dielectric behaviour of the diamond films were discussed in detail.