Heteroepitaxy of gallium nitride on (0001), (1012) and (1010) sapphire surfaces

The structure, surface morphology and photoluminescence properties for the undoped GaN films grown on the (0001), (1012) and (1010) α-Al₂O₃ substrates have been investigated using the halide vapor phase epitaxy (HVPE) method with the Ga/HCl/NH₃/He system. X-ray diffratometer (XRD), reflection high energy electron diffraction (RHEED) and scanning electron microscopy (SEM) are used for the study of the structure and surface morphology of the film. The luminescence property is assessed by photoluminescence (PL) measurement at room temperature. The following orientation relationships are observed; (0001) GaN/(0001) Al₂O₃, (1120) GaN/(1012) Al₂O₃, and (1013) and (1212) GaN/(1010) Al₂O₃. The (1013) GaN films possess two types of surface morphology depending upon the growth conditions. A possible reason for this phenomenon is discussed. The optimum growth conditions of the GaN films for each orientation are established. The qualities of the films showing different orientations are compared. For the (1013) GaN films, it is observed that the higher the growth temperature, the better the crystal structure and the smoother the surface morphology. The relative intensities of (1212) and (1013) films grown at higher temperature are much lower by several ten times than those of (0001), (1120) and (1013) GaN film grown at lower temperature.