Investigation On Fabrication And Optoelectical Properties Of N-doped ZnO Thin Films Grown In Rich Zn Condition

Since the realization of stimulated emission of ZnO films at room temperature by optical pumping in 1996, researches on ZnO and its related materials have become one of the most promising and attractive aspects in the ultraviolet light emitting devices, detectors and lasers due to its wide band gap of 3.37eV at RT and larger exciton binding energy of 60 meV.The unintentionally doped ZnO usually has n-type conduction due to the native defects (VO, Zni), so far the fabrication of p-type ZnO becomes a bottleneck of research on ZnO-based materials. Therefore, the growth of high quality p type ZnO is a very attentive hotspot of study in ZnO. In this thesis, we investigated to how to reproduce p-type ZnO thin films through analysis of the experience conditions and obtained weak p-type ZnO thin films by the plasma-molecular beam epitaxy (P-MBE) after reproduction of high quality ZnO films grown on Al₂O₃. Then we research the doping mechanism bout p-type ZnO material based on the weak p-type ZnO films grown by MBE. The details are as follows:(1) The N-type ZnO thin films on sapphire substrate were prepared by P-MBE using NO as both O and N dopant source in the rich-Zn condition. As-grown ZnO has a n-type conduction with high carrier concentration. The temperature variation of resistivity from the sample shows metallic conducting behavior. The conducting mechanism of ZnO thin films grown in rich Zn condition was studied by the measurement of the crystalline structure, the optical and electrical properties.(2) After the as-grown samples were annealed at 500℃in oxygen ambient, the conduction type of the sample transformed from n-type to p-type. The physical mechanism of p-type ZnO was investigated by X-ray diffraction, X-ray photoemission spectrometer, absorption and photoluminescence spectra, and Hall -effect measurement.