Advances in the Realisation of GaN-Based Microcavities: Towards Strong Coupling at Room Temperature
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Advances in the Realisation of GaN-Based Microcavities: Towards Strong Coupling at Room Temperature F. SEMOND, D. BYRNE, F. NATALI. M. LEROUX, J. MASSIES, N. ANTOINE-VINCENT1, A. VASSON1, P. DISSEIX1, and J. LEYMARIE1 CRHEA-CNRS, Rue Bernard Grégory, Sophia-Antipolis, F-06560 Valbonne, France. 1 LASMEA-UMR 6602 UBP/CNRS, Université Blaise Pascal – Clermont-Ferrand II, F-63177 Aubière cedex, France. ABSTRACT In a recent paper [Phys. Rev. B 68, 153313 (2003)], we reported the first experimental observation of the strong coupling regime in a GaN-based microcavity. The λ/2 GaN optical cavity was grown by molecular beam epitaxy on a Si(111) substrate. The upper mirror is a SiO2/Si3N4 dielectric mirror and the silicon substrate acts as the bottom mirror. With such a relatively simple and low-finesse microcavity, a Rabi splitting of 31 meV was measured at 5K. On the basis of this very encouraging result, approaches to fabricate high-finesse GaN-based cavities exhibiting strong coupling with stable polaritons at room temperature are discussed. INTRODUCTION In semiconductor microcavities, strong exciton-photon coupling regime can be achieved forming new quasi-particles, called cavity-polaritons which are part exciton, part photon [1]. The energies of the two polariton modes anticross when the energy difference between exciton and photon modes is varied. The minimum polariton splitting, called “vacuum Rabi splitting”, measures the strength of the coupling. Polaritons have many favourable properties, moreover recent results show that polaritons in microcavities can exhibit dynamic condensation [2] which is expected to open the route for a new generation of optoelectronic devices [3]. Most of the advances in polariton physics have been achieved in GaAs/AlGaAs based structures but, in order to demonstrate polariton-based devices operating at 300K, material systems having a large exciton oscillator strength and binding energy are needed [3]. The high oscillator strength enables a large Rabi splitting (the polariton splitting is proportional to the square root of the oscillator strength of the excitonic transition) while the high exciton binding energy is also essential for the stability of excitons at high temperatures and densities. Table I compares the exciton binding energies and vacuum Rabi splittings reported for various material systems. It is important to note that for GaAs [4,5], CdTe [6] and ZnSe [7] based microcavities, Rabi splitting values are measured experimentally while for GaN-based microcavities, they are only calculated [8,9]. It is seen from Table I that the exciton binding energy in GaN-based microcavities combined with their expected large coupling strength (both are greater than kBT at 300K (25meV)) should produce robust polariton states stable at room temperature. Therefore GaNbased microcavities are potentially interesting to fabricate a new generation of optoelectronic polariton devices. However, despite the fact that interesting results have been obtained in the last years concerning the growth o
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