Growth of non-polar InGaN quantum dots with an underlying AlN/GaN distributed Bragg reflector by metal-organic vapour phase epitaxy

Non-polar (11-20) InGaN quantum dots (QDs) have been grown using a modified droplet epitaxy method by metal-organic vapour phase epitaxy on top of a 15-period AlN/GaN distributed Bragg reflector (DBR) on a-plane GaN pseudo-substrate prepared by epitaxial lateral overgrowth (ELOG), in which the QDs are located at the centre of a ca. 180 nm GaN layer. The AlN/GaN DBR has shown a peak reflectivity of ∼80% at a wavelength of ∼454 nm with a 49 nm wide, flat stop-band. Variations in layer thicknesses observed by cross-sectional scanning transmission electron microscopy have been identified as the main source of degradation of the DBR reflectivity. The presence of trenches due to incomplete coalescence of the ELOG template and the formation of cracks due to relaxation of tensile strain during the DBR growth may distort the DBR and further reduce the reflectivity. The DBR top surface is very smooth and does not have a detrimental effect on the subsequent growth of QDs. Enhanced single QD emission at 20 K was observed in cathodoluminescence.