Point-Defect Distribution and Transformation Near the Surfaces of AlGaN Films Grown by MOCVD

The characteristics of vacancy-type point defects near the surface and inside the AlGaN films were studied by positron annihilation spectroscopy (PAS) and fluorescence spectra. Two types of AlGaN films were grown by varying the growth temperature and the Si doping to maintain the volume of the threading dislocation densities (TDs). The PAS results showed that the point-defect types of the AlGaN films with approximate TDs differed. In the detailed PAS results, the W-S curves of AlGaN films showed two types of point-defect distribution forms. One type was uniform in the AIGaN film, namely, the major point defects inside the bulk and near the surfaces are almost the same as that of the V-III-O-N complex, which was the probable candidate. The other type was nonuniform, suggesting that the major point defects were V-Ga/V-Al inside the bulk and V-III-nO(N) complexes near the surfaces of the AlGaN films. The evolution of the PAS and fluorescence spectra also suggested that a point-defect rearrangement occurred near the surfaces of the AlGaN films after 10 MeV high-energy e-beam irradiation. This rearrangement was likely related to the transformation of the point-defect type from the oxide-substituted nitride (O-N) to the oxide vacancy (V-O, equaling to V-N) based on our growth recipes.