Résumé
Self-assembled semiconductors QDs are of great interest in fundamental physics as well as inapplied physics. In GaN/AlN heterostructures, the huge band-offset and the strong excitonicbinding lead to an important exciton confinement allowing an emission even at roomtemperature. GaN QDs grown along the (1000) axis are named “polar” due to their stronginternal electic field which lead to the so-called QCSE. The most important modifications due tothis electric field take place in thick QDs emitting around 330nm and more : the luminescence isredshifted and the radiative lifetime is strongly increased [1]. On the other hand, in thin QDs(smaller than 2.3nm), the quantum confinement plays the key role, thus leading to a significantlysmaller homogeneous linewidth and to the resolution of the exciton fine-structure splitting[2]. Concerning the radiative recombination processes, several papers reported measurements at330nm or more either in polar[3] or non-polar[4] nanostructures. Experimental data on excitonicradiative lifetime are also existent in thin QDs but on a limited dynamical range where thepossible influence of QCSE is not discussed [5].In this work, we report time-resolved photoluminescence measurements in GaN/AlN QDsemitting between 280nm and 360nm. For QDs emitting at 300nm we observe a biexponentialdecay dynamics of the photoluminescence signal (Fig.1, left). The fast component (450 ps) isinterpreted as the radiative lifetime of the QDs in the absence of a noticeable redshift of thetransition. Thanks to our better signal-to-noise ratio than in Ref. 5, we are able to extract a slowcomponent (2 ns) which may originate either from feeding from the barrier or other processesinside the QD. Power dependent experiments further confirm this interpretation. We observe thatthe fast component remains the same as a function of excitation power (Fig.1, right) and, moreimportantly, that the intensity ratio keeps the same value. This rules out any contribution fromthe relaxation of multi-carriers complexes such as biexciton or trion in the short time dynamics