Excitons in nitride heterostructures: From zero- to one-dimensional behavior

Description

We report an unusual temperature dependence of exciton lifetimes in arrays of GaN nanostructures grown onsemipolar (11-22) oriented Al0.5Ga0.5Nalloy by molecular beam epitaxy.Atomic force microscopy measurementsrevealed: (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] crystallographicaxes. As a consequence, a morphological transition from dot-shaped islands forming an array of nanochains towire-shaped objects elongated along the [1-100] direction was evidenced with the increase of the GaN depositedamount. Nanostructures of different dimensionality were fabricated including quantum dots (QDs), quantumwires (QWRs), and quantum wells (QWs), and the excitonic behavior was investigated as a function of thenanostructure shape. The measured temperature dependencies of the exciton radiative decay revealed its directcorrelation with a spatial confinement, resulting in a temperature-independent exciton lifetime in the case ofQDs, a square root dependence in the case of QWRs, and a linear dependence for QWs. These results, as well asabsolute values of measured lifetimes, are in agreement with theoretical predictions.

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