Morphological Evolution of the InGaN-Based Quantum Well Surface due to a Reduced Density of Threading Dislocations in the Underlying GaN through Higher Growth Pressure

We have examined how fewer threading dislocations (TDs) in an underlying GaN epilayer affects the surface morphology of InGaN/InGaN quantum well (QW) structures grown by low-pressure metalorganic vapor phase epitaxy. When the GaN growth pressure was raised from 100 Torr to 400 Torr, the density of pure edge and mixed character TDs was reduced due to the low-density formation and increase in the size of initially grown GaN islands. However, the density of pure screw TDs simultaneously increased. The QW surface morphology strongly depended on the densities of mixed or screw TDs in the underlying GaN epilayer. We found that the pit density in the surface of the QW structure decreased with a lower density of mixed TDs, and that the QW surface morphology then exhibited a pattern of large nanoscale islands if the density of screw TDs simultaneously increased, or a pattern of heavily bunched steps if it was unchanged.