High resolution transmission electron microscopy and three-dimensional atom probe microscopy as complementary techniques for the high spatial resolution analysis of GaN based quantum well systems

GaN based light emitting diodes containing InxGa1-xN quantum wells represent a successful and broadly commercialised optoelectronic technology. However, significant questions remain regarding their surprisingly bright and long lived luminescence given the high densities of threading dislocations which they contain. The threading dislocations' limited impact is due to localisation of excitons in the quantum wells, preventing their diffusion to dislocation cores. However, the nature of the localisation sites is unclear. Transmission electron microscopy studies suggested that gross indium clustering occurs at a similar to 3 nm scale. Here, the authors will review the evidence and show that such gross indium clusters are an artefact of electron beam damage, and that three-dimensional atom probe studies reveal InxGa1-xN to be a random alloy. However, fluctuations in quantum well width either at the few nanometre or the broader (50-100 nm) lateral scale, or both, may contribute to localisation and hence to improved device performance.