Energy band formation in ZnO/AlOx superlattices and white luminescence
W.C. Hsieh1*, P.V. Wadekar1,2, H.C. Huang4, Q.Y. Chen1,2, Y.T. Lin1, H.J. Chen1, C.F. Chang1, Y.H. Tu1, W.C. Sung1, C.M. Shiau1, Y.S. Hong1, P.C. Kung1, Y.P. Cheng1, C.Y. Dang1, C.H. Lee1, C.W. Tseng3, W.C. Chou3, L.W. Tu1, N.J. Ho4, W.K. Chu2
1Physics, National Sun-Yat Sen University, Kaohsiung, Taiwan
2Physics, University of Houston, Texas, USA
3Electrophysics, National Chiao Tung University, Hsin-Chu, Taiwan
4Material Science, National Sun-Yat Sen University, Kaohsiung, Taiwan
* presenting author:Wan-Chen Hsieh,
ZnO/AlO superlattices of various layer thicknesses and periodicities were deposited by atomic lay-er deposition (ALD) on (0001)-oriented Al2O3 substrates at 450K using diethyl zinc (DEZ), trime-thyl aluminum (TMA) and H2O as precursors for Zn, Al and O, respectively. The superlattices consist of 30 cycles of ZnO, and the AlO cycles vary from 1 to 10. From X-ray Reflectivity (XRR) and cross-section TEM imaging, the sample thickness, interface roughness, and possible interface diffusion could be characterized. The epitaxial qualities of all the samples were verified by the standard three-step criteria of X-ray diffraction (XRD). According to the XRD results, the epitaxial superlattices take the wurzite structure of ZnO as a whole, and are purely c-oriented, as judged by the lack of peaks in the grazing-incidence XRD (GIXRD) patterns and the 6-fold symmetry ofφ-scans. For those of thicker AlO, the ZnO layers of the superlattices become polycrystalline while the AlO layers become amorphous. Photoluminescence spectra show that the samples of 1-cycle of Al, i.e., one monolayer of AlO, have the widest spectral range of luminescence in the visible region, hinting at promising application possibilities for white luminescence.

Keywords: ZnO, Superlattices, Atomic Layer Depositon, Photoluminescence, X-ray Diffraction