The optical absorption spectra of the N vacancy, VN, in proton-irradiated AlxGa1–xN samples were observed. The spectra which were obtained for samples with x-values of between 0.55 and 1 exhibited a peak and a shoulder, with their energy positions dependent upon the Al mole fraction. The peak and shoulder in the optical absorption spectra were interpreted as being transitions from the valence band to the VN energy levels located below the conduction band in samples with x-values greater than 0.55. These results were used to extrapolate the VN energy level positions in samples with x-values of between 0 and 0.55. A linear fit of the observed VN energy level (eV) yielded:

E(VN) = 4.230 + 0.680x

for all values of x. Thermal annealing of various samples showed that the total integrated area, which was directly proportional to the defect density of the absorption band attributed to the N vacancy, decreased as the annealing temperature was increased.

Observation of Nitrogen Vacancy in Proton-Irradiated AlxGa1–xN. Q.Zhou, M.O.Manasreh, M.Pophristic, S.Guo, I.T.Ferguson: Applied Physics Letters, 2001, 79[18], 2901-3