X-ray photoelectron spectroscopy evaluation on surface chemical states of GaN, InGaN and AIGaN heteroepitaxial thin films grown on sapphire by MOCVD

The surface chemical states of MOCVD grown GaN, A1GaN and InGaN, and the influence of different dopants have been studied with x-ray photoelectron spectroscopy (XPS). The results show that for most of the samples the N ls peak can be fitted with a dominant GaN peak at the binding energy of 397.2 ± 0.2 eV and a small N-H peak at the binding energy of 398.5 ± 0.2 eV, while Ga 3d can be deconvoluted into three peaks, i.e., elemental Ga at 18.5 ± 0.1 eV, GaN at 19.7 ± 0.1 eV, and Ga₂O₃ at 20.4±0.1 eV. Si-doping appears to have small influence on the surface chemical states of GaN. Compared with Sidoping, the influence of Mg-doping appears to be larger. In addition to a change in the component intensities, Mg-doping also causes the N ls and Ga 3d peaks to broaden. The ternary Al_xGa_l-xN (x ∼0.025) sample shows aluminum surface segregation, while the undoped In_xGa_l-xN (x ∼0.12) shows indium surface deficiency.