Identification of the deep level defects in AlN single crystals by electron paramagnetic resonance

Electron paramagnetic resonance (EPR) at 9.4 and 35 GHz were studied on two types of AlN single crystals, grown by a sublimation sandwich method. These investigations revealed the presence of transition metals impurities in the first sample: Fe 2 + ( S = 2 ) and some paramagnetic centers with S = 3 / 2 , we suggest Cr 3 + or Ni 3 + as the possible candidates. The EPR spectra of Fe 2 + were observed up to the room temperature. After sample illumination at 5 K with light (wavelength shorter 700 nm) strong EPR signal with a g factor of shallow donors (SDs) and slightly anisotropic linewidth appears. This light-induced EPR signal, once excited at low temperature, still persists after switching off the light and is about constant up to 30 K then it drops quickly. SDs show a negative correlation energy U and oxygen in the N position ( O N ) is the most probable model. EPR spectra of deep-donor center which was assumed to be the nitrogen vacancy V N have been observed in the second sample. The x-ray irradiation leads to considerable enhancement of deep donor's ( V N ) signals intensity. The annealing resulted in recombination thermoluminescence and the deep donor ( V N ) energy level was estimated to be about 0.5 eV. The models of shallow ( O N ) and deep ( V N ) donor centers were supported by comprehensive hyperfine structure analysis.