We report an unusual temperature dependence of exciton lifetimes in arrays of GaN nanostructures grown on semipolar (11-22) oriented Al${}_{0.5}$Ga${}_{0.5}$N alloy by molecular beam epitaxy. Atomic force microscopy measurements revealed: (i) a one-dimensional ordering tendency along the [1-100] crystallographic direction together with (ii) an in-plane anisotropy of the nanostructure lateral shape with respect to [1-100] and [11-23] crystallographic axes. As a consequence, a morphological transition from dot-shaped islands forming an array of nanochains to wire-shaped objects elongated along the [1-100] direction was evidenced with the increase of the GaN deposited amount. Nanostructures of different dimensionality were fabricated including quantum dots (QDs), quantum wires (QWRs), and quantum wells (QWs), and the excitonic behavior was investigated as a function of the nanostructure shape. The measured temperature dependencies of the exciton radiative decay revealed its direct correlation with a spatial confinement, resulting in a temperature-independent exciton lifetime in the case of QDs, a square root dependence in the case of QWRs, and a linear dependence for QWs. These results, as well as absolute values of measured lifetimes, are in agreement with theoretical predictions.

• Received 19 April 2013

DOI:https://doi.org/10.1103/PhysRevB.88.125437