Reduction in surface defects on red-emitting InGaN quantum wells by using vicinal GaN (0001) surfaces

This study demonstrates a substantial reduction in surface defects on red-emitting InGaN quantum wells (QWs) by using vicinal GaN (0001) surfaces. Red InGaN QWs are grown on GaN on sapphire (0001) substrates with off-angles of 0.3° or 1.0° toward the [11¯00] direction using metal-organic vapor phase epitaxy. The GaN underlayer on the 0.3°-off substrate exhibits a smooth surface, whereas that on the 1.0°-off substrate exhibits step bunching, resulting in micrometer-scale spatial variations in local off-angles. Surface defects of small V-pits, large V-pits surrounded by anomalous growth islands, and trench defects are densely distributed across the entire area of the InGaN QWs grown on the 0.3°-off templates. In contrast, the QWs on the 1.0°-off templates exhibit reduced densities of both anomalous growth islands and trench defects in regions with local off-angles exceeding ∼1°. These results indicate that preferential step-flow growth on vicinal surfaces with high step densities, which inherit the atomic ordering of the underlayers, suppresses the formation of basal stacking faults associated with trench defects and of anomalous growth islands. A part of the defect-reduced regions on the 1.0°-off templates exhibit enhanced red-emission intensities compared with the QWs on the 0.3°-off templates with high defect densities. This partial improvement indicates the presence of nonradiative recombination centers related to the surface defects and other defects such as edge dislocations or point defects.