Polarization-dependent XEOL: Comparison of peculiar near-band-edge emission of non-polar alpha-plane GaN and ZnO wafers

Abstract

Polarization-dependent hard X-ray excited optical luminescence (XEOL) spectroscopy was used to study the properties of near-band-edge (NBE) emission of non-polar alpha-GaN and alpha-ZnO wafers. We found similar behaviors of alpha-GaN with alpha-ZnO that include the positive intensity jump and the blue shift of the NBE emission peak in the XEOL spectrum following the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Ga or Zn K-edge. Furthermore, as the X-ray energy is set above the K-edges, different oscillations of XEOL, also following the XANES, were observed depending upon the directions of the excitation X-ray electric field. However, the blue shift of alpha-ZnO is about two times larger than that of alpha-GaN that results from the larger polar field in alpha-ZnO than that in alpha-GaN. For both alpha-GaN and alpha-ZnO, the above K-edge excited oscillations in XANES and XEOL spectra, where the polarization is set parallel to the pi-axis, are attributed to simultaneous excitations of the p-bond along the pi-axis and in-plane sigma-bonds, whereas only the in-plane sigma-bonds are excited for the polarization perpendicular to the pi-axis. Therefore, these polarization dependent oscillation features of XEOL yields that follow the fluorescence yields can be used as an alternative way to determine the crystallographic orientations. Published under license by AIP Publishing.