(a) 2 μm×2 μm AFM image of the surface morphology of c-plane GaN grown under a V/III atom ratio of 1940 and temperature of 915 °C (Sample G). (b) 2 μm×2 μm AFM image of the surface morphology of c-plane GaN grown under a V/III atom ratio of 2945 and temperature of 865 °C (Sample C). Surface pits are located at the intersections of surface steps. The pits are connected with screw type dislocation determined from the cross-sectional weak beam dark-field TEM images taken in the same region but using different diffraction conditions. (c) and (d) g = 1120 near the [1100] zone axis, since screw dislocation only appears under according to the invisible criteria. (e) 2 μm×2 μm AFM image of the surface morphology of c-plane GaN grown under a V/III atom ratio of 2945 and temperature of 915 °C (Sample B). Surface pits become less distinguished. (f) 2 μm×2 μm AFM image of the surface morphology of c-plane GaN grown under a V/III atom ratio of 2945 and temperature of 965 °C (Sample A). Pit size becomes slightly larger with the further elevation of temperature. (g) A pit is vaguely observed under the enlarged view of the bright-field TEM image (inset). Cross-sectional two-beam bright-field TEM images of the sample taken in the same region of the pit but under different diffraction conditions (g) g = 0002 and (h) g=1120 near the [1100] zone axis. The pit position is indicated by the white dashed frame.