The morphologies of GaN crystals grown on Ga- and N-face of HVPE seeds by the Na flux liquid phase epitaxial method

GaN crystal growth on Ga-face and N-face of HVPE-GaN seeds was investigated using Na flux liquid phase epitaxial (LPE) method, respectively. The phase structure and morphology of as-grown GaN crystals were characterized using X-ray diffraction (XRD) and the scanning electron microscope (SEM), respectively. Under the growth temperature of 850 °C and keeping nitrogen pressure 3.0 MPa for 150 h, the typical pyramidal GaN poly-crystals with wurtize structure grew by spontaneous nucleation growth on the Ga-face of GaN -HVPE seeds. In contrast, GaN single crystals could be obtained by epitaxial growth on the N-face of GaN-HVPE seeds. From the observation of the side view of as-grown GaN crystals grown on the N-face, there were two apparent stages along the growth direction (-c direction) during the crystal epitaxial growth process. The typical hexagonal layered structure of as-grown GaN crystals occurred in the initial stage, and then the typical hexagonal pyramidal structure of it occurred in the second growth stage. In addition, from the observation of optical microscope, the as-grown GaN crystal with the initial growth stage only presented different morphology from that with the two-growth stage. The continuous lateral equilibrium epitaxial growth on N-face of GaN crystal seed may be of great significance for the growth of large size GaN single crystal.