Electron paramagnetic resonance techniques were used to investigate defects in hexagonal BN, polycrystalline cubic BN, and pure BN or C-doped BN films which had been produced by reactive sputtering. The predominant paramagnetic center in the hexagonal material was deduced to be the N vacancy. The zincblende samples exhibited a single resonance line, and a model for the predominant paramagnetic defect could not be formulated. However, under the assumption that the N vacancy in this material was again responsible for the observed resonance, an estimate of the electron density at the B nuclei of the first coordination shell was obtained from the experimental data. It was found that films which were produced by using up to 10%N2 in Ar discharges exhibited single-line electron paramagnetic resonance signals with a g-value and line-width that were consistent with those observed for high-pressure cubic BN. The spin concentration was reduced upon increasing the N pressure in the discharge; thus supporting the identification of the paramagnetic center as being a N vacancy. Films which were produced using N partial pressures in the Ar discharge that were greater than 10% exhibited an increased spin density. This was inconsistent with the idea that N incorporation reduced the number of N vacancies. The BN films degraded in time, when exposed to the atmosphere, and this was attributed to the presence of H3O+ or other complex defects which involved H and/or O. Doping with C increased the spin density and the g-value, and this supported the suggestion that C stabilized the electron in the N vacancy. The spin-lattice relaxation rates exhibited an unusual and almost linear temperature dependence. It was concluded that theoretical analysis of the electronic structure of the defects might clarify whether excited states of defects within the phonon spectrum existed and permitted an Orbach relaxation process. This would then explain the observed temperature dependence.

M.Fanciulli: Philosophical Magazine B, 1997, 76[3], 363-81