Observation of nitrogen vacancy in proton-irradiated AlxGa1−xN

The optical absorption spectra of nitrogen vacancy (VN) in proton-irradiated AlxGa1−xN samples are observed. The spectra obtained for samples with 0.55⩽x⩽1 exhibit a peak and a shoulder with their energy positions dependent on the Al mole fraction. The peak and shoulder in the optical absorption spectra were interpreted as transitions from the valence band to the VN energy levels located below the conduction band in samples with x0.55. The results were used to extrapolate the VN energy level positions in samples with 0⩽x⩽0.55. A linear fit of the observed VN energy level yields E(VN)=4.230+0.680x (eV) for all values of x. Thermal annealing of various samples shows that the total integrated area, which is directly proportional to the defect density, of the absorption band attributed to the nitrogen vacancy is decreased as the annealing temperature is increased.