L - Mbe Epitaxial Growth Of Gan Film Prepared By The Study

Due to excellent characteristics, GaN wide bandgap semiconductor can meet the requirments of blue-violet light-emittin, detector, high-temperature, high-speed, high frequency and high power devices. The niobate management (LiNbO3) single crystal is an excellent ferroelectric, piezoelectric and pyroelectric, which is widely used in the field of surface acoustic wave, non-volatile storage, optical modulators and optical switches, etc. GaN/LiNbO3integrated thin films are conducive to the development of multi-functional and miniaturized devices. However, duo to different physical and chemical properties, it’s difficult to integreate GaN on LiNbO3. Meanwhile, due to the complexity of the hetero-epitaxial process, the limitations of the experiental conditions and theoretical studies, many of the phenomena and the physical mechanism have not been in-depth study. Especially, researches on GaN thin film heteroepitaxial growth mechanism and thin film microstructure control are limit.With its similar lattice structure and low cost advantages, sapphire is used to the most common substrate for heteroepitaxial GaN film in industry. It is industrial and science significant to study the mechanism of hetero-epitaxial and growth behaviors. In this paper, GaN thin films were fabricated by laser molecular beam epitaxy equipment. The process parameters of GaN grown on sapphire and on niobate substrates were optimized. High-quality GaN epitaxy thin films were fabricated at lower temperatures respectively. GaN thin film heteroepitaxial mechanism and microstructure control in different mismatch system and temperatures were studied.(1) High-quality epitaxial GaN films on sapphire substrates were fabricated successfully with the optimal conditions of700℃substrate temperature, the2Hz laser frequency and the180mJ laser energy. With the smooth hexagonal islands surface and good crystallization, GaN thin film finally grown in layer by layer mode. GaN films have good in-plane symmetry and were epitaxied with the30°rotation on sapphire substrate.The epitaxial relationship is GaN(0002)[1120]//sapphire(0001)[1010].(2) The two-step growth of GaN thin film technology:First60nm-thickness GaN thin film was grown at700℃, then continue to grow50nm-thickness GaN films in 550℃, can effective improve the crystalline quality and surface roughness of the GaN films. Out-plane FWHM reduced to0.435°. GaN have better in-plane symmetry than before. This technology is different from the mechanism of AlN and GaN-low temperature buffer.(3) After annealing four hours at the high temperature of1000℃in the LiNbO3single crystal box, LiNbO3substrate surface formated step flow, achieved atomically flat scale and avoided LiNb3O8phase to reduce the problem of Li elements volatilize in the heating process. Thus, annealing reduced the interfacial diffusion and improved the crystalline quality of epitaxial GaN films.(4) The high-quality epitaxial GaN films were fabricated on the LiNbO3single crystal substrate at650℃. GaN thin film grown in layer by layer mode with the smooth surface (RMS=0.97nm) and good crystallization (out-plane FWHM=0.499°). GaN films have good in-plane symmetry and were epitaxied with the30°rotation on LiNbO3substrate, the epitaxial relationship is GaN(0002)[1120]//LiNbO3(0006)[1010]. GaN thin films have the least amount of non-doped N-vacancy and intrinsic defects at650℃.(5)Study hetero-epitaxial growth and microsturcture control of GaN according to interface energy conversion, island migration and the effect of growth temperature on crystal defects theoreties. The study found that:the large lattice mismatch and the changing from interfacial stress energy into surface free energy contributed to GaN films grown in3D mode; Enough surface evolution contributed by Migration、 combination and lower barrier of the island side is a necessary condition for growth mode changed from3D to2D; GaN films kept growing on3D mode at low temperatures; Wth temperature lower by lower, the intrinsic such as crystal sector bit wrong defects and non-doped N-vacancy defects density were increased, GaN thin films have a more rough surface, and lower crystalline quality.