Probing the excitonic states of site-controlled GaN nanowire quantum dots.

We report the detection of fully confined excited states and the zero-absorption region of individual site-controlled GaN/AlGaN nanowire quantum dots using photoluminescence excitation spectroscopy, which provides evidence of the true zero-dimensional discrete density of states of such quantum dots. Because of the strong quantum confinement in these dots, the p-shell, d-shell, and even higher energy (including some f-shell) states of a single quantum dot are observed, which provides unprecedented insight into the electronic structure. Several emitters are measured and used to build up an average picture of the electronic structure of a single quantum dot via comparison to theoretical simulations.