The crystal structure of a-plane GaN/ZnO heterostructures on r-plane sapphire was investigated by using the XRD and TEM measurment. It was found the formation of (220) ZnGa2O4 and crystal orientation of semipolar (10$\bar 1$3) GaN at GaN/ZnO interface. The epitaxial relation of normal surface direction are the sapphire (1$\bar 1$02) // a-GaN (11$\bar 2$0) and ZnGa2O4 (220) // semi-polar GaN (10$\bar 1$$\bar 3$). Beside, the emission peak energy of ZnO appears shift about 60 meV in the GaN/ZnO/GaN heterostructures due to the re-crystallization of ZnO layer with Ga or N atom and the formation of the localized state.

We studied the polarization-dependent photoluminescence (PL) of a-plane GaN /AlGaN multiple quantum wells (MQWs) grown on r-plane sapphire substrate with the various well width from 1.5 to 7.33 nm. To clarify the reasons of light emission polarization properties, we applied the 6×6 k‧p model to simulate the E-k dispersion relation and the wave functions to obtain the polarization optical transitions. According to the experimental result, the PL emission peak position exhibits a red-shifted with increasing well width, due to the reduction of the quantum confinement effect. The polarization ratio of a-plane GaN/AlGaN MQWs increased from 0.236 to 0.274 with increasing the quantum well width. This phenomenon is believed to be that y-polarized light emission gradually dominates the PL spectrum and thus enhances the polarization ratio.

We reported the systematical study of optical properties of hexagonal AlxGa1-xN epitaxial films grown on c-sapphire substrate using metal-organic chemical vapor deposition. By performing Fourier transform infrared spectroscopy measurements, the high-frequency dielectric constants and phonon frequencies can be obtained by theoretically fitting the experimental infrared reflectance spectra using a four-phase layered model. The high-frequency dielectric constant of AlxGa1-xN varies between 4.98 and 4.52 for ε∝,│(polarization perpendicular to the optical axis) and between 4.95 and 4.50 for ε∝,//(polarization parallel to the optical axis) respectively when the aluminum composition changes from 0.15 to 0.24. Furthermore, from experimental infrared reflectance spectra of AlxGa1-xN films, a specific absorption dip at 785 cm-1 was observed when the aluminum composition is larger than 0.24. The dip intensity increases and the dip frequency shifts from 785 to 812 cm-1 as aluminum composition increases from 0.24 to 0.58. According to the reciprocal space map of x-ray diffraction measurements, the emergence of this dip could be resulted from the effects of strain relaxation in AlGaN epitaxial layers due to the large lattice mismatch between GaN and AlGaN epitaxial film.

We report the experimental observation of a very strong cavity polariton dispersion in a multi-axial mode GaN microcavity. The linewidth of photoluminescent (PL) spectrum covers a few cavity axial modes. The resonant photoluminescent peaks have a strong dispersion. The frequency spacing between adjacent peaks decreases by almost a factor of five from 470nm to 370nm. The strong dispersion can be well described by cavity polariton dispersion, but not by the dispersion of the refractive index of GaN. The measured exciton-photon interaction constant is 260 meV. It is an order of magnitude higher than the typically reported values for GaN microcavities

In this work, we report on the growth of ultraviolet (UV) AlGaN/GaN multiple quantum wells (MQWs) structure using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW sample grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers comprised AlN/GaN superlattices (SLs). The root-mean-square value of the surface morphology was only 0.35 nm observed from the atomic force microscope image and no crack was found on the surface. Both of the high resolution X-ray diffraction curves and transmission electron microscope images showed sharp interfaces between SLs layers and QWs with good periodicity. These results demonstrate that the ALD could be a very useful technique for controlling the crystalline quality and thickness of the III-nitride epilayer.

The general approximate solutions for the two-dimensional thermoelastic problems with a nearly circular hole are provided in this study. Based on Stroh formalism and the method of conformal mapping, the boundary perturbation analysis is applied to solve the problems of a hole with arbitrary shape. The radius of the hole considered here is represented as a sum of a reference constant and a perturbation magnitude that is expanded into a Fourier series. In order to illustrate the applicability and efficiency of the present approach, special examples associated with polygonal hole problems are solved explicitly and discussed in detail. Since the general solutions have not been found in the literature, comparison is made with some special cases for which the analytical solutions exist, which shows that our proposed method is effective and general.

The thermoelastic problem associated with a point heat source embedded in an anisotropic body containing an elliptic hole or a rigid inclusion is considered in this paper. By using the formalism of Stroh [1], the approach of analytic function continuation and the technique of conformal mapping, the expression for the temperature, displacements and stress functions is expressed in explicit matrix form. The present derived solutions are also valid for some special problems such as a crack or a rigid line inclusion if one lets the minor axis of the ellipse approach to zero. The stress intensity factors induced by a point heat source are also obtained.