Optical spectroscopy of InGaN-GaN quantum dot ensembles

InGaN-GaN quantum dots (QDs) have been grown, with variations in the deposition time used to vary the properties of the dots. Atomic force microscopy (AFM) studies of uncapped dots indicate a small increase in dot density with increasing deposition time. Photoluminescence (PL) spectroscopy at low temperatures reveals a red shift of the dot emission as the deposition time is increased. Power dependent PL measurements indicate that it is relatively easy to saturate the QD ground state emission because of their low density and expected long carrier lifetime. Emission from an excited state is observed for high excitation powers. With increasing deposition time the activation energy which determines the high temperature quenching of the dot PL is found to increase. Photoluminescence excitation (PLE) reveals a continuum of states below the GaN band edge which is attributed to the presence of a wetting layer.