| dc.description.abstract | Metal organic chemical vapor deposition (MOCVD) is the most popular fabrication method for the crystalline GaN thin film. However, the disadvantages of MOCVD are its high process temperature and the high cost. In this study, a fabrication method high-power impulse magnetron sputtering(HiPIMS) with low-temperature and low-cost are applied to deposit GaN films.
Silicon is one of the attractive substrate materials for GaN, the deposition of thin films with the advantages of low cost and thermal stability at high growth temperatures. But due to the large lattice constant mismatch (16.9%), it is almost impossible to deposit a GaN thin film on the silicon substrate directly. A suitable buffer layer is necessary in between the GaN and the silicon substrate to improve the quality. The lattice constant difference between ZnO and GaN is only 1.8%. So ZnO was used in this research as the buffer layer to improve the crystalline quality of the GaN films.
After depositing the ZnO buffer layer, a thermal annealing process was applied. According to the XRD and SEM analysis, the FWHM of the annealed ZnO(0002) XRD spectrum was decreased from 0.201° to 0.182°, and the crystal grains became larger, indicating that the crystal quality was improved. However, the surface roughness (RMS) was also increased from 3.59 nm to 13.4 nm.
According to the SEM measurement and analysis, the larger the crystal grains of the ZnO buffer layer, the larger the crystal grains of the GaN film. According to the TEM measurement and analysis, when the GaN film was deposited on the ZnO buffer layer, the crystal direction of GaN could grow along the crystal direction (0002) of the ZnO buffer layer. Based on the above measurement and analysis, the better the crystalline quality of the ZnO buffer layer, the better the crystalline quality of the GaN thin film. Therefore, the future work of this research is to improve the surface roughness of the ZnO buffer layer after the annealing, and then it is possible to improve the quality of the GaN films. | en_US |