Improvement in crystal quality of GaN films with quantum dots as buffer layers grown on sapphire substrates by molecular beam epitaxy

This paper reports the improvement in the crystal quality of GaN films by using multiple layers of quantum dots (QDs) as part of a strain-relieving buffer layer in molecular beam epitaxy. Two sets of GaN samples were grown on c-plane sapphire substrates, one included a buffer containing a few AlN and GaN layers grown at different temperatures and another set contained a buffer layer into which additional QD structures were inserted. As compared to samples without QDs, samples with QDs generally showed narrower X-ray diffraction peaks and higher photoluminescence efficiency. The density of dislocations was examined by pit revealing wet chemical etching and AFM imaging. It was found that insertion of multiple GaN/AlN QD layers into the buffer layer effectively reduces the density of dislocations in the epitaxial layers. Compared to dislocation densities similar to10(10)cm(-2) typically observed in GaN films grown on AlN buffer layers, a density of similar to5x 10(7) cm(-2) was demonstrated in the GaN films grown on GaN/AlN multiple QD layers.