1. Key Laboratory of Luminescence and Optical Information，Ministry of Education，Institute of Optoelectronic Technology, Beijing Jiaotong University，Beijing 100044，China 2. School of Science，Tianjin Polytechnic University，Tianjin 300160，China 3. School of Material Science and Engineering, Beijing University of Aeronautics & Astronautics, Beijing 100083, China 4. School of Science, Lishui University, Lishui 323000, China
Abstract：High-quality ZnO thin films were grown by plasma-assisted molecular beam epitaxy (P-MBE) on Al2O3(0001) substrate with a low temperature ZnO buffer layer. Structural and optical characterization were studied for ZnO thin films. Only a peak at (0002) were observed in the X-ray reflectivity(XRD) spectra with the full-width at half maximum (FWHM) value 0.18°, and two peaks 1LO(579cm-1) and 2LO(1 152 cm-1) were detected in the resonance Raman scattering spectra at room temperature. These results indicated that ZnO thin films had single orientation of c axis and high-quality of crystal wurtzite structure. The absorption of free-exciton and exciton-LO phonon appeared in the absorption spectra, which confirmed that the exciton state in the ZnO thin films were stable even at room temperature. And the energy spacing between these two peaks is 71.2 meV, corresponds to the longitudinal optical phonon energy of 71 meV of ZnO. Besides, from the photoluminescence spectra, no defect-related deep emission were observed, but just a remarkable free-exciton emission located at 376nm were obtained at room temperature, it proved that the ZnO thin films had high-quality but low density of defect.
[1] Jeon H, Ding J, Nurmikko A V, et al. Appl. Phys. Lett., 1990, 57：2413. [2] Nakamura S, Senoh M, Nakahana S, et al. Appl. Phys. Lett., 1996, 69：1477. [3] SHANG Hong-kai, ZHANG Xi-qing, YAO Zhi-gang, et al(商红凯，张希清，姚志刚，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析),2006,26(3)：415. [4] MEI Zeng-xia, ZHANG Xi-qing, WANG Zhi-jian, et al(梅增霞，张希清，王志坚，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析),2003,23(3)：461. [5] Chen Y, Tuan N T, Segawa Y, et al. Appl. Phys. Lett.,2001, 78：1469. [6] Sun H D, Makino T, Segawa Y, et al. Appl. Phys. Lett.,2001, 78：3385. [7] Ohtomo A, Tamura K, Saikusa K, et al. Appl. Phys. Lett., 1999, 75：2635. [8] Zhang X H, Liu Y C, Wang X H, et al. J. Phys.: Condens. Matter,2005, 17: 3035. [9] Zhang X T, Liu Y C, Zhi Z Z, et al. J. Phys.D: Appl. Phys.,2001, 34：3430. [10] Chen X B, Morrison J L, Huso J, et al. Mater. Res. Soc. Symp. Proc.，2005, 831：615. [11] ōzgür ü, Alivov Y I, Liu C, et al. J. Appl. Phys.,2005, 98：041301. [12] Demangeot F, Paillard V, Chassaing P M, et al. Appl. Phys. Lett.,2006, 88：071921. [13] Shimomura T, Kim D, Nakayama M. J. Lumin.,2005, 112：191. [14] Cho S, Ma J, Kim Y, et al. Appl. Phys. Lett., 1999, 75：2761. [15] Kim S S, Lee B T. Thin Solid Films,2004, 446：307. [16] Chen Y F, Hong S K, Ko H J, et al. Appl. Phys. Lett.,2000, 76：245.
