Magnetic resonance studies of point defects in diamond

Abstract

Electron paramagnetic resonance (EPR) has been used to study point defects in synthetic single crystal diamond. Newly observed defects are reported in high pressure high temperature (HPHT) and chemical vapour deposition (CVD) diamond. HPHT diamond doped with 15N has been used to investigate the g = 2 region of the EPR spectrum which is obscured when natural isotopic abundances are present. Two previously unreported defects labelled WAR9 and WAR10 are reported. The EPR data has been shown to be consistent with the neutral nitrogen interstitial, N0 I (WAR9), and neutral nitrogen di-interstitial, NI-I001 (WAR10), defects respectively. Two further defects observed in CVD diamond are reported here. The first labelled WAR2 is preferentially aligned with the direction of growth, [001]. The EPR data is consistent with a (V-(CH)-V)0 structure although theoretical studies suggest that this structure is unstable at CVD growth temperatures. Growth mechanisms are suggested that would account for the observed preferential alignment. The second defect labelled WAR5, has been observed exclusively in samples grown using an experimental CVD chemistry containing oxygen. The EPR data is consistent with the OV0 defect, although no confirming 17O hyperfine structure has been observed. 13C hyperfine data is also reported for the KUL1/VnH− defect (n = 1 or 2) but the new data is not sufficient to conclusively discount either the n = 1 or n = 2 models suggested for this defect. Changes in defect concentrations in CVD diamond with thermal and illumination treatments has been investigated. Experimental data has indicated the presence of an unseen trap, common to CVD diamond, with concentrations comparable to that of N0S, and levels in the band-gap 0.5{1.2 eV above the top of the valence band. The difficult quantification of sub part per billion defect concentrations, as observed in electronic grade material, is tackled with the use of rapid passage EPR. It is shown that with this technique it is possible to detect concentrations of single nitrogen in diamond at tens of parts per trillion, close to a factor of 100 improvement on the currently used slow passage EPR