Browsing by Author "Wu, Jian-Xing"

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Peculiar near-band-edge emission of polarization-dependent XEOL from a non-polar a-plane ZnO wafer
(2018-02-05)
Lin, Bi-Hsuan
;
Wu, Yung-Chi
;
Chen, Huang-Yeh
;
Tseng, Shao-Chin
;
Wu, Jian-Xing
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 2p pi-bond along the c-axis and the bilayer sigma-bond, whereas only the sigma-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. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Probing the exciton-phonon coupling strengths of O-polar and Zn-polar ZnO wafer using hard X-ray excited optical luminescence
(2016-11-07)
Lin, Bi-Hsuan
;
Chen, Huang-Yeh
;
Tseng, Shao-Chin
;
Wu, Jian-Xing
;
Chen, Bo-Yi
The temperature-dependent hard X-ray excited optical luminescence (XEOL) spectroscopy was used to study the optical properties of O and Zn polarity of a c-plane single crystal ZnO wafer. By analyzing the XEOL and XRD, we found an unprecedented blue shift of the free exciton transition with increasing the excited carrier density as tuning the X-ray energy across the Zn K-edge, and the O-polar face possesses better crystal structure than the Zn-polar one. This spectral blue shift is attributed to the Coulomb screening of the spontaneous polarization by the excited free carriers that result in decreasing the exciton-phonon Frohlich interaction to reduce exciton binding energy. Published by AIP Publishing.