Open AccessPeculiar near-band-edge emission of polarization-dependent XEOL from a non-polar a-plane ZnO wafer
Author(s) -
BiHsuan Lin,
YungChi Wu,
Huang-Yeh Chen,
ShaoChin Tseng,
JianXing Wu,
Xiaoyun Li,
Bo–Yi Chen,
Chien-Yu Lee,
GungChian Yin,
Shian-Wen Chang,
MauTsu Tang,
Wen–Feng Hsieh
Publication year - 2018
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.26.002731
Subject(s) - xanes , materials science , excited state , polarization (electrochemistry) , exciton , blueshift , molecular physics , photoluminescence , atomic physics , spectral line , optoelectronics , chemistry , condensed matter physics , physics , astronomy
Polarization-dependent hard X-ray excited optical luminescence (XEOL) was used to study not only the optical properties but also the crystallographic orientations of a non-polar a-plane ZnO wafer. In addition to a positive-edge jump and extra oscillations in the near-band-edge (NBE) XEOL yield, we observed a blue shift of the NBE emission peak that follows the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Zn K-edge. This NBE blue shift is caused by the larger X-ray absorption, generating higher free carriers to reduce the exciton-LO phonon coupling, which causes a decrease in the exciton activation energy. The extra oscillations in XANES and XEOL as the polarization is set parallel to the c-axis is attributed to simultaneous excitations of the Zn 4p - O 2pπ -bond along the c-axis and the bilayer σ-bond, whereas only the σ-bond is excited when the polarization is perpendicular to the c-axis. The polarization-dependent XEOL spectra can be used to determine the crystallographic orientations.