Room temperature Strong coupling in low finesse GaN microcavities
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Room temperature Strong coupling in low finesse GaN microcavities I. R. Sellers*, F. Semond, M. Leroux and J. Massies. CRHEA-CNRS, Rue Bernard Gregory, Parc Sophia Antipolis, Valbonne 06560, France P. Disseix, G. Malpuech, A-L. Henneghien, J. Leymarie and A. Vasson LASMEA, Université Blaise Pascal, Clermont Ferrand II, Les Cézeaux, 63177 Aubière Cedex, France. ABSTRACT We present experimental results demonstrating strong-light matter coupling at low and room temperature in bulk GaN microcavities. Angle dependent reflectivity measurements demonstrate strong-coupling with a Rabi-energy of 50meV at room temperature which is well reproduced with transfer matrix simulations. The absence of strong coupling in the photoluminescence is attributed to the low finesse of the microcavity (Q=60) and is confirmed by simulations which indicate a quality factor of 90 is required to observe strong-coupling in the emission. INTRODUCTION In recent years there has been intensive research into the field of light-matter interaction in semiconductor microcavities, and in particular the so-called strong coupling regime [1, 2]. Strong-coupling occurs when excitons and photons with the same energy and momentum strongly interact to create quasi-particles, which are neither exciton nor photon, but rather the eigenstates of the both. This creates a number of interesting physical properties not possible for excitons and photons alone. The advantage of the nitride materials for microcavities is they offer the possibility to observing strong coupling at 300K as a result of the large exciton binding energy and oscillator strengths of these systems [3]. EXPERIMENTAL DETAILS In this paper we present a bulk λ/2-GaN microcavity grown by molecular beam epitaxy on a 7 period epitaxial AlN/Al0.2Ga0.8N Distributed Bragg Reflector (DBRs) grown directly on silicon (111). The complete growth technique of (0001) oriented nitrides on silicon is described elsewhere [4]. After the growth of the GaN active layer on the DBR, the microcavity structure was completed with the deposition of a 10nm transparent aluminium mirror. DISCUSSION Figure 1(a) shows the reflectivity spectra of the microcavity for various angles of incidence from 5º to 60° at 5K for TE polarisation. Also shown in Figure 1(a) is PL at 5K measured prior to the deposition of the aluminium film. The PL emission peaks at 3.51eV which is high in comparison to conventional µm-thick GaN on silicon that emits at ~3.46 eV at 12K [4] and results from the large biaxial compressive strain within the λ/2 GaN
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layer (~66 nm) due to the AlN/(Al,Ga)N DBR upon which it is grown. The main image in Figure 1(a) shows the TE polarised angle resolved reflectivity at 5K. At an angle of 5° three features are clearly observed in the reflectivity. The optical mode can be observed at ~3.463 eV negatively detuned with respect to the A and B-free excitonic features observed at 3.521 eV and 3.533 ± 0.002 eV respectively. The observation of highly resolved A and B free excitons in the reflectivit
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