Potentialities of GaN-based microcavities in strong coupling regime at room temperature.
Résumé
In a recent publication [N. Antoine-Vincent, F. Natali, D. Byrne, A. Vasson, P. Disseix, J. Leymarie, M. Leroux, F. Semond, J. Massies, Phys. Rev. B 68 (2003) 153313], we have highlighted for the first time the exciton–photon strong coupling in a GaN-based microcavity and obtained a Rabi splitting of 31 meV persistent at 77 K. Our aim is now to study the feasibility of GaN-based microcavities for which the strong coupling regime would be maintained at room temperature. A complex heterostructure containing GaN/AlGaN quantum wells (QWs) is investigated by photoreflectivity and reflectivity at 5 K. The QW thickness is 3 nm and the Al composition and thickness of the barriers are respectively 0.11 and 10 nm. From the modeling of the experimental spectra, the values of the oscillator strength, the energy and the broadening parameter of the QW fundamental transition are determined; the broadening is found to be relatively weak (15 meV). Simulations of microcavities containing QWs have then been performed including this set of parameters: a theoretical Rabi splitting of 34 meV is obtained at 5 K. Considering an additional broadening induced by the increase of the temperature (23 meV), the strong coupling regime could be maintained theoretically at room temperature in such a structure. This is due to the low value of the inhomogeneous broadening related to the QW transition which is lower than in bulk GaN. The influence of the QW number and the nature of the Bragg mirror on the Rabi splitting is then discussed in realistic structures.