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

Abstract

A comparison of the various aspects of current research on exciton dynamics in GaN-based epitaxial layers is proposed. To date, most contributions have been concerned by: (1) micrometric epitaxial layers of GaN, the physics of which is essentially devoted to the identification and control of non-radiative processes; (2) InGaN/GaN multiple quantum wells, for which several hypotheses are currently competing for explaining the very long decay times observed, related to strong localization effects. It has been shown by reviewing recent research that the temporal behaviour of radiative recombinations in these systems is ruled by hardy controlled factors, whereas the physics of low-dimensional excitons in GaN/GaAlN quantum wells is closer to that in the model system GaAs/GaAlAs. Measurements of the decay times of free and 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 polaritons. The low-temperature limit of this lifetime is deduced to be much smaller than in GaAs/GaAlAs quantum wells, and consistent with a longitudinal–transverse splitting of 0.6 meV. The theoretical analysis of relative decay times of free excitons and localized states indicates that the latter correspond to electrons and holes having localization radii smaller than the Bohr radius.