Structure Study Of GaN/Al₂O₃ By High Resolution X-ray Diffraction

In recent years, GaN-based optoelectronic materials and devices have been rapidly developed, however, there has not full studied in GaN thin films. Many theoretical and experimental studies should be focused on the GaN-based materials and properties, especially these problems affected industrialization. So far, almost all of the published papers are regarded on the density of threading dislocations in GaN. Many studies have been done on different approaches studied the density of threading dislocations of GaN, such as Transmission electron microscopy (TEM), X-ray diffraction(XRD), but the results which measured by these approaches are not consistency with luminescence.In this thesis, on the basis of analysis the advantages and disadvantages of the usual approaches, high-resolution X-ray diffraction was used to analyze the GaN layers grown on sapphire by metal-organic chemical vapor deposition (MOCVD), such as the crystal structures, the misorientation angle between the GaN epilayer and Sapphire substrate, the accurate lattice constants of GaN films, the bending radius of the wafers and stress of GaN films and dislocation densities . The main content of this thesis and some main conclusions are as follows:1, The diffractograms(20/ω-scans) of all samples only have (00.2), (00.4) diffraction peak in the direct mode indicated that the GaN films are wurtzite structure and strongly c-oriented. The GaN thin films are not parallel Sapphire substrate and misorientation has exactly came into being between them. The measured c lattice constant by eliminated the instrument's error is larger than that of body single crystal GaN which indicates that the films are under the compressive stress.2, The measuring method of the accurate crystal constants was discussed basing on the substrate peak of the X-ray high intensity diffraction spectrum and the errors induced by misorientation must be deducted. The measured a lattice constant is less than that of body single crystal GaN and c is larger, which also indicates that the films are under the compressive stress. This compressive stress is derived from the lattice and thermal mismatch.3, Misorientation was exactly assuredly came into being between the GaN epilayer and Sapphire substrate by X-ray high intensity mode diffraction measurement. The misorientation azimuth angle is nearly same with the miscut azimuth of sapphire...