Recombination dynamics of excitons in III-nitride layers and quantum wells

A comparison of the various aspects of current research on exciton dynamics in GaN-based epitaxial layers is proposed. To date, most contributions hav e been concerned by: (1) micrometric epitaxial layers of GaN, the physics o f which is essentially devoted to the identification and control of non-rad iative processes; (2) InGaN/GaN multiple quantum wells, for which several h ypotheses are currently competing for explaining the very long decay times observed, related to strong localization effects. It has been shown by revi ewing recent research that the temporal behaviour of radiative recombinatio ns in these systems is ruled by hardy controlled factors, whereas the physi cs of low-dimensional excitons in GaN/GaAlN quantum wells is closer to that in the model system GaAs/GaAlAs. Measurements of the decay limes of free a nd localized excitons in GaN/GaAlN quantum wells, versus temperature T, are presented. The radiative lifetime of free excitons increases linearly with T, in agreement with available theories on bidimensional excitonic polarit ons. The low-temperature limit of this lifetime is deduced to be much small er than in GaAs/GaAlAs quantum wells, and consistent with a longitudinal-tr ansverse splitting of 0.6 meV. The theoretical analysis of relative decay t imes of free excitons and localized states indicates that the latter corres pond to electrons and holes having localization radii smaller than the Bohr radius. (C) 1999 Elsevier Science S.A. All rights reserved.