Surface superstructures and optical properties of wurtzite GaN grown on 6H-SiC

We report on the surface reconstructions on the basal planes of wurtzite GaN. Depending on the surface polarity, two distinct classes of reconstructions form. The Ga-polar surface displays the Ga fluid-1 ×1, 10 × 10, 5,√3 × 2√13, 5 × 5, 4 × 4, and 2 × 2, and the (0 0 0 1) N-polar surface the 6 × 8, 6 × 6, √7 × √7 and 2 × 3 with decreasing surface Ga coverage. We will show that their structure is consistent with a simple Ga-adatom-based scheme. Crystalline structure and optical properties of the GaN epilayers are examined by high resolution X-ray diffraction and photoluminescence, and the results reveal a strong relation between the threading-dislocation density and the intensities of both near-band transition at 3.427eV and yellow luminescence at 2.16eV.