| The optoelectronic devices of ultraviolet detector, transducers, short-wavelength light emitting and laser diode etc, have extensive application in optical communication, optical memory, display etc. And the wide band gap semiconductor materials, such as ZnO, are a good candidate for it, therefore, the research of ZnO has become the hot topic both here and abroad.However, there are still two key problems before the extensive application of ZnO series optoelectronic device, one is the p-tipe doping, and the other is about the energy band matching. To solve these two key problems, high quality ZnO thin films grown are required. In this work, high quality ZnO thin films, grown on highly mismatched sapphire (0001) substrates, are researched by using the radio frequency plasma-assisted molecular beam epitaxy ( rf-MBE ) . And the growth conditions, structural and optical properties of ZnO thin films are characterized. We also study the influence of growing conditions to the photoluminescence of ZnO thin films to obtain the parameters of high quality single crystal ZnO thin films growth. By studying the influence of rf power and O2 flux to the ZnO thin films, optimal condition are gained: rf power 300W, O2 flux 1.8sccm and substrate temperature 650℃. The samples growth according to these condition we obtained have highly (0002) oriented, the FWHM value of XRD (0002) peak is just 0.18°. Moreover, in the resonant Raman scattering study, two peaks 1LO ( A1 ) and 2LO are found in the Raman spectra, these result indicate that the ZnO thin films have single c axis oriented and high quality wurtzite structure. The absorption of free exciton and exciton-LO phonon peaks are also detected in the absorption spectra, it imply that the exciton of ZnO thin films are stable even at RT. In the Photoluminescence spectra, only a free exciton emission peak is observed at 376nm under room temperature, showing that the ZnO thin films have high quality and low defect density. |
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