Defect reduction in (112¯) a-plane GaN by two-stage epitaxial lateral overgrowth

Abstract

The authors report a two-stage epitaxial lateral overgrowth (ELO) method to get uniformly coalesced (112¯0) a-plane GaN using metal organic chemical vapor deposition by employing a relatively lower growth temperature in the first stage followed by conditions leading to enhanced lateral growth in the second. Using a two-stage ELO method the average Ga-polar to N-polar wing growth rate ratio has been reduced from 4–6 to 1.5–2, which consequently reduced the height difference between the two approaching wings at the coalescence front that resulted from the wing tilt (0.44° for Ga and 0.37° for N wings, measured by x-ray diffraction), thereby making their coalescence much easier. Transmission electron microscopy showed that the threading dislocation density in the wing areas was 1.0×108cm−2, more than two orders of magnitude lower than that in the window areas (4.2×1010cm−2). However, high density of basal stacking faults of 1.2×104cm−1 was still present in the wing areas as compared to c-plane GaN where they are rarely observed away from the substrate. Atomic force microscopy and photoluminescence measurements on the coalesced ELO a-plane GaN sample also indicated improved material quality.