Radiative lifetime of excitons in high energy GaN/AlN quantum dots

Julien Selles (1) , Guillaume Cassabois (1) , Thierry Guillet (1) , Fabrice Semond (2)

1 L2C - Laboratoire Charles Coulomb
2 CRHEA - Centre de recherche sur l'hétéroepitaxie et ses applications

Self-assembled semiconductors QDs are of great interest in fundamental physics as well as in applied physics. In GaN/AlN heterostructures, the huge band-offset and the strong excitonic binding lead to an important exciton confinement allowing an emission even at room temperature. GaN QDs grown along the (1000) axis are named “polar” due to their strong internal electic field which lead to the so-called QCSE. The most important modifications due to this electric field take place in thick QDs emitting around 330nm and more : the luminescence is redshifted 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 significantly smaller homogeneous linewidth and to the resolution of the exciton fine-structure splitting[2]. Concerning the radiative recombination processes, several papers reported measurements at 330nm or more either in polar[3] or non-polar[4] nanostructures. Experimental data on excitonic radiative lifetime are also existent in thin QDs but on a limited dynamical range where the possible influence of QCSE is not discussed [5]. In this work, we report time-resolved photoluminescence measurements in GaN/AlN QDs emitting between 280nm and 360nm. For QDs emitting at 300nm we observe a biexponential decay dynamics of the photoluminescence signal (Fig.1, left). The fast component (450 ps) is interpreted as the radiative lifetime of the QDs in the absence of a noticeable redshift of the transition. Thanks to our better signal-to-noise ratio than in Ref. 5, we are able to extract a slow component (2 ns) which may originate either from feeding from the barrier or other processes inside the QD. Power dependent experiments further confirm this interpretation. We observe that the fast component remains the same as a function of excitation power (Fig.1, right) and, more importantly, that the intensity ratio keeps the same value. This rules out any contribution from the relaxation of multi-carriers complexes such as biexciton or trion in the short time dynamics

Domaines: Autre [cond-mat.other]

Julien Selles, Guillaume Cassabois, Thierry Guillet, Fabrice Semond. Radiative lifetime of excitons in high energy GaN/AlN quantum dots. Condensed Matter Day, Semiconductors I: Coherence properties in semiconductor quantum dots, Aug 2014, Paris, France. ⟨hal-01132335⟩