Preparations And Properties Of ZnO/AlN Bilayer Thin Films

ZnO is a wide direct band gap (3.37eV) semiconductor with high excition binding energy of 60meV. Because of its excellent electrical, optical, piezoelectric, gas-sensitive, pressure-sensitive properties and high thermal stability, it possesses broad applications in various fields such as gas-sensitive devices, surface acoustic wave devices and pressure-sensitive devices. At present, due to the great mismatch parameters in lattice constants and thermal expansion coefficient between Si and ZnO, it is difficult to achieve high-quality epitaxial growth of ZnO thin films, so a buffer layer of AlN is used.In chapter 1, the crystalline structure, properties, all kinds of preparing methods, the potential applications about ZnO thin films are introduced.In chapter 2, we systematically introduced the theory and process of radio frequency(RF) magnetron sputtering and ion beam deposition sputtering(IBD). The preparations of AlN buffer layer and ZnO thin film were introduced in detail. Finally, we summarized the characterization techniques used in our experiment.In chapter 3, we studied the RF magnetron sputtering process of AlN buffer layers, at the same time the influences of working pressure, substrate, sputtering time and anneal temperature on the structure of AlN buffer layers were induced. The surface morphologies of the samples deposited with different working pressure were studied too. The results indicate that the AlN buffer layers deposited with the working pressure of 0.2Pa can be used to get the ZnO/AlN bilayer films with a highly c-axis(002) orientation.In chapter 4, the ZnO/AlN bilayer thin films were prepared by RF magnetron sputtering, and the crystalline structure, surface morphologies and photoelectric properties of the samples were studied. Compared with ZnO thin films prepared with the same process, the bilayer films have lower stress, larger average grain size, lower mean square root roughness and electrical resistivity. When the sputtering time of AlN buffer layers is 60min and 90min respectively, the bilayer films have higher quality. The room-temperature fluorescence spectrums show that all samples have a UV intrinsic peak near 372nm and blue emission peaks near 440nm and 464nm. The green emission peaks are not observed. Because the intensity ratio between intrinsic peak and blue emission peaks is bigger, the qualities of ZnO/AlN bilayer thin films with AlN buffer layer prepared for 60min and 90min are better.In chapter 5, the ZnO/AlN bilayer thin films were prepared by IBD and anneal in O₂. The crystalline structure and photoelectric properties of the samples were studied. Compared with littery growth orientation of ZnO single layer thin films prepared with the same process, ZnO/AlN bilayer thin films deposited by IBD exhibit a orientation along c-axis(002). Its electrical resistivity is lower. The room-temperature fluorescence spectrums show that both ZnO/AlN bilayer thin films and ZnO single layer thin films have a UV intrinsic peak and blue emission peaks, meanwhile green emission peak is observed in the spectrum of ZnO single layer thin films.