| dc.description.abstract | In this research, a thin (60-100 nm) ZnO layer deposited by sputtering is employed as the buffer layer for the epitaxial growth of GaN on (100) Si substrates. The ZnO buffer mitigates the huge lattice mismatch between GaN and Si, and therefore is expected to improve the crystal qualities of GaN. The orientation of the sputtered ZnO thin film is along the c-axis according to X-ray diffraction (XRD) ω-2θ measurements. During the growth of GaN in the metal organic chemical vapor deposition (MOCVD) system, the important parameters include substrate temperature, growth duration, reactor pressure and V/III ratio. The morphology of GaN epilayers are analyzed by scanning electron microscope (SEM) and atomic force microscopy (AFM). It is found that polycrystalline GaN micro-trapezoids are formed on the ZnO buffer, which is believed to stem from the unique rod-like ZnO nanostructure produced by the sputtering process.
In addition to the c-plane ZnO buffer, m-plane ZnO layer is also prepared in this project. The goal of m-plane ZnO buffer is to build nonpolar InGaN multiple quantum wells, in which the radiative recombination efficiency can be enhanced by eliminating the undesired quantum-confined Stark effect (QCSE). The m-plane ZnO layer is realized by a post-annealing at 850 °C after the sputtering process, followed by the hydrothermal regrowth of ZnO at 90 °C for 2 hours. Preliminary results show that the orientation of the ZnO layer is strongly dependent on layer thickness, post-annealing temperature, annealing environment, and the conditions of the hydrothermal regrowth. | en_US |