The role of V-shaped pits in (AlGaIn)N LED structures

Despite the high density of threading dislocations generally found in group-III-nitride semiconductors, the light emission efficiency of GaInN/GaN quantum well (QW) structures is exceptionally high at room temperature. Therefore, nonradiative recombination processes of charge carriers in a QW must be suppressed. This can be explained by our V-shaped pit model, where every threading dislocation is decorated with a hexagonal V-shaped pit. The QWs inside a V-shaped pit are thinner compared with the QWs on c-plane. Thus the effective band gap is significant larger and the charge carriers will be kept away from the threading dislocations. In our GaInN/GaN QW structures with high internal quantum efficiency we find in TEM well-controlled V-shaped pits around the dislocations. In order to clarify the situation for commercial devices we investigated blue and green LEDs from various suppliers. We find that V-shaped pits are decorating virtually all threading dislocations in the QW region. This indicates that suppression of nonradiative recombination by V-shaped pits may be a desirable mechanism for achieving high light emission efficiency. We also discuss the effect of pits in GaN/AlGaN QW structures, where the typical emission efficiency is much lower than for GaInN/GaN structures