In this thesis, we grew the LiAlO2 single crystals was grown by Czochralski method and determined the best polishing process. The raw materials of growing LiAlO2 are Li2CO3 and Al2O3. After mixing these two powders, they are put into an Ir crucible and heat it up with RF generator in N2 environment. We tried to use the optimized rotation rate and pull rate in the growth process to ensure the shape of the crystal to be uniform and having the good quality. Before the epitaxy of GaN, the substrate must be polished to improve GaN quality. The (100) surface of LiAlO2 was polished by using various particle size of SiC sandpapers, de-ion water mixed with Al2O3 powders, and colloidal SiO2 suspension. Finally, the LiAlO2 specimen is soaked into an acid solution for etching at room temperature to obtain a smooth surface. The results show a roughness below 1.0 nm rms.

We invistegated the characteristic of GaN grown on LiAlO2 substrate by molecular epitaxy beam. First of all , we try to changed the growth ratio and concluded some relation between the quality of thin film. We expect to improve the quality of M-plane GaN and the size and density of c-plane GaN single-crystals by changing growth conditions. we found that when the N / Ga flow ratio decreased, that is much favor to the growth of M-plane GaN, is not favor to the growth of c-plane GaN. Further research indicates that, on entering the PA-MBE growth prior to phosphoric acid ratio of 1:50 with water to etch the surface of LAO substrate for a minute, is more suitable for M-plane GaN growth, can effectively inhibit Growth of c-plane GaN. The last series of samples, we will LAO substrate into PA-MBE system, DI water before soaking for ten minutes, we found the study can help to improve the c-plane GaN growth.

We invistegated the characteristic of GaN grown on LiAlO2 substrate by molecular epitaxy beam. We observed the c-plane GaN crystalls assembled at the step-edge of M-plane GaN terraces, with 200 nm ~ 600 nm diameter and 300 nm height. Furthermore, we also observed that there are two kinds of formations for c-palne GaN: one is grown from the hexagonal plane of LAO, the other is transformed from the defeat of M-plane GaN. In addition, we changed the growth ratio and concluded some relation between the quality of thin film and roughness of surface. We expect to improve the quality of M-plane GaN and the size and density of c-plane GaN single-crystals by changing growth conditions.

In this thesis, we investigated the growth of nonpolar GaN on (100) £^¡VLiAlO2 substrate by a simple chemical vapor deposition (CVD) process. Metallic gallium, NH3 and ultra-purity nitrogen were used as Ga, N sources and carrier gas. The X-ray diffraction and scanning electron microscopy were used to study the influence of growth conditions such as reaction pressure, growth temperature and deposition time on the GaN epilayer¡¦s orientation and surface morphology. It¡¦s found that pure c plane, c mixed m plane and pure m plane GaN epilayers can be grown on LiAlO2 substrates by the change of growth temperatures (950¢XC~1050¢XC) under 200 torr pressure and NH3/N2 (450/450sccm) gas flow. In addition, with longer deposition time (30min ~120min), nonpolar GaN epilayers show better crystal quality. Furthermore, atomic force microscopy, Raman spectroscopy, cathodeluminescence, transmission electron microscopy were used to study the surface morphology, stress, optical properties and microstructure of the nonpolar GaN epilayers.

A hydride vapor phase epitaxy, (HVPE) was designed to grow nonpolar GaN. LiAlO2 single crystal grown by Czochralski (Cz) method in our lab was used as the substrate. The X-ray diffraction and scanning electron microscopy were used to study the GaN epilayer¡¦s orientation and surface morphology. At the first part, we used the c-plane sapphire as substrate and make sure that our HVPE reactive system is working. And the second part, we used LiAlO2 substrate to grow non-polar GaN substrate. After the growth, GaN was separated from LiAlO2 substrate and become free-standing. We found that as-grown GaN has both c-plane (0001) and m-plane (10-10) orientations. After some improvements, we got a nonpolar GaN substrate. But the m-plane (10-10) GaN grains are random. The photo-luminescence¡]PL¡^showed that the light emissive quality of these two GaN thick film are well. We will keep improving the design of our HVPE.

The group III nitride semiconductor grown on c-plane sapphire by radio frequency plasma assisted molecular beam epitaxy has been studied. To archive good quality GaN thin film, nitridation and low temperature AlN buffer layer were applied to overcome the issue of lattice mismatch. Low temperature and long period nitridation process shows better improved of optical properties and crystal quality of GaN film. Buffer layer grown with slightly Ga-rich, substrate temperature at 600¢J, for 20 minutes leads to better GaN thin film. High substrate temperature and sufficient nitrogen to gallium ratio are two important factors to control the growth of the good quality GaN epilayer. We have grown M-plane GaN films with self-assembled c-plane GaN nanopillars on a £^-LiAlO2 substrate by plasma-assisted molecular-beam epitaxy. The diameters of the basal plane of the nanopillars are about 200 to 900 nm and the height is up to 600 nm. The formation of self-assembled c-plane GaN nanopillars is through nucleation on hexagonal anionic bases of £^- LiAlO2. Dislocation defects were observed and analyzed by transmission electron microscopy. From the experimental results, we developed a mechanism underlying the simultaneous growth of three-dimensional c-plane nanopillars and two dimensional M-plane films on a £^-LiAlO2 substrate.

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Both non-polar (10-10) (m-plane) and polar (0001) (c-plane) zinc oxide (ZnO) have a good lattice match with lithium aluminum (LiAlO2, LAO) (200) substrate, so it is difficult to control the epitaxial orientation. Therefore, this research is to explore how the growth parameters influence on the crystal orientation of ZnO film grown by plasma assisted molecular beam epitaxy. The experimental results show that m-plane ZnO can be grown with low zinc flux and low oxygen pressure. Increasing zinc flux and oxygen pressure will lead to increase in growth rate, and consequently, c-plane ZnO will nucleate on the substrate besides m-plane zinc oxide. The substrate temperature is one of the main factors that influence the choice of zinc oxide epitaxial orientation. High temperature will promote the m-plane zinc oxide nucleation, while low temperature will conduct to the c-plane zinc oxide nucleation. Under low zinc flux and low oxygen pressure, epitaxy of ZnO with different crystalline orientations can be achieved through changing the substrate temperature. The surface morphology and roughness of the substrate will affect the particle size and surface morphology of ZnO epilayers. When the substrate is smooth, the crystal size of the epitaxial film is large and the surface is flat with many rectangular stripes, taking on the platform-like morphology. If the substrate is rough with many scratches, the particle size becomes small and the surface is granular-like and rather rough. Furthermore, when the substrate is rough, it is difficult to control the different orientations of ZnO epitaxial films through changing the substrate temperature.

Gamma-phase lithium aluminate (LiAlO2) single crystal is grown by Czochralski pulling method and a-plane LiAlO2(LAO) is chosen as the substrate for subsequent gallium nitride (GaN) epitaxial growth by plasma-assisted molecular beam epitaxy (PAMBE). The lattice mismatch between the nitride and the substrate is greatly reduced due to small lattice mismatch of~0.3% between [0001]GaN and [010]LAO and of~1.7% between [11-20]GaN and [001]LAO in the plane of the substrate LAO(100). Pure hexagonal [10-10]GaN is successfully grown directly on the LAO substrate without buffer layer. Crystal quality and properties are analyzed through a series of measurements, including reflection high-energy electron diffraction (RHEED), field-emission electron microscopy (FESEM), electron backscatter diffraction (EBSD), x-ray diffraction and cathodo luminescence (CL).