Defect reduction in (11-20) a-plane GaN by two-step epitaxial lateral overgrowth

Abstract

ABSTRACTWe report a two-step growth method to obtain uniformly coalesced epitaxial lateral overgrown a-plane GaN by metalorganic chemical vapor deposition (MOCVD). By obtaining a large wing height to width aspect ratio in the first step followed by enhanced lateral growth in the second step via controlling the growth temperature, we reduced the tilt angle between the advancing Ga-polar and N-polar wings for improved properties. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing area was 1.0×108cm−2, more than two orders of magnitude lower than that in the window area (4.2×1010cm−2). However, a high density of basal stacking faults, 1.2×104cm−1, was still observed in the wing area. Near field scanning optical microscopy (NSOM) at room temperature revealed that the luminescence was mainly from the wing regions with very little contribution from the windows and meeting fronts. These observations suggest that due to significant reduction of threading dislocations radiative recombination is enhanced in the wings.