Structural characterization of non-polar (1 1 2 0) and semi-polar (1 1 2 6) GaN films grown on r-plane sapphire

Thick GaN films, with (1 1 2 0) or (1 1 2 6) planes parallel to the r-plane of sapphire, were grown by molecular beam epitaxy using AlN or GaN buffer layers. Characterization by transmission electron microscopy revealed a high density of basal-plane stacking faults (BSFs) in the (1 1 2 0) non-polar GaN (a-GaN) films. {1 1 2 0} and {1 0 1 0} prismatic-plane and {1 1 0 2} pyramidal-plane stacking faults (SFs) were observed to terminate some BSFs. The SFs on {1 0 1 0} and {1 1 0 2} planes generally formed closed domains. For (1 1 2 6) semi-polar GaN (s-GaN) films, most threading dislocations were located at small-angle grain boundaries. Many BSFs were observed close to the AlN/GaN interface but, in comparison with a-GaN, the s-GaN films had much lower BSF density at the top surface. Inversion domain boundaries (IDBs) on {1 0 1 0} planes were observed to form closed domains. GaN/AlGaN multiple quantum wells (MQWs) grown on s-GaN or a-GaN followed the morphology of the GaN surface. Some IDBs in the s-GaN propagated through the GaN/AlGaN MQWs to the top surface.