2D XAFS–XEOL Mapping of Ga_1–xZn_xN_1–xO_x Nanostructured Solid Solutions

Abstract

We have applied two-dimensional X-ray absorption fine structure–X-ray-excited optical luminescence (2D XAFS–XEOL) and X-ray absorption near-edge structure (XANES) spectroscopy to study the nature of the X-ray-excited optical luminescence process in GaN–ZnO solid-solution nanostructures, both indium-doped (GIZNO) and undoped (GZNO). XAFS–XEOL analysis of GZNO reveals that X-ray-excited optical luminescence (XEOL) is a strong function of the excitation energy, and hence penetration depth, as well as the turn-on of any shallow core levels. Indium K-edge XANES results reveal that indium in GIZNO forms a surface oxide but has limited solubility in the solid solution. This observation is consistent with the morphology change from nanoparticles in GZNO to nanosheets in GIZNO induced by the presence of a surface In layer, which ultimately becomes oxidized to form In2O3. XAFS–XEOL measurements suggest that the XEOL from GIZNO is primarily due to oxygen defects in the indium oxide surface layer and effective energy transfer from the GaN–ZnO solid solution.