Excitons in nitride heterostructures: From zero- to one-dimensional behavior
Résumé
We report an unusual temperature dependence of exciton lifetimes in arrays of GaN nanostructures grown on
semipolar (11-22) oriented Al0.5Ga0.5Nalloy 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.