I. R. Sellers

Strong light-matter coupling at room temperature in simple geometry GaN microcavities grown on silicon

The reflectance spectra of simple design GaN-based microcavities have been studied in the 5 K–300 K range. The epitaxial structure consists of the silicon substrate and the stack of buffer layers as the back mirror, a GaN active layer, and a 100 A thick aluminium layer as the top mirror. Active layer thicknesses of λ∕2, λ, or 3λ∕2 were investigated. The samples with GaN thicknesses λ∕2 and λ display an anticrossing behavior between the cavity and exciton modes, with measured Rabi splittings of 47 and 60 meV, respectively, both at 5 K and room temperature.

Polariton relaxation bottleneck and its thermal suppression in bulk GaN microcavities

We discuss the presence of a polariton bottleneck in bulk GaN microcavities. Angle resolved photoluminescence measurements were performed using low excitation power densities for several negative detunings between the exciton and photon modes. At low temperatures, we observe an enhancement in the emission intensity at angles corresponding to the anticrossing of the lower and upper polariton modes, a clear demonstration of the polariton relaxation bottleneck. This feature becomes less prominent with increasing temperature, eventually disappearing at room temperature. We conclude that polariton-acoustic phonon scattering is the dominant polariton relaxation mechanism in bulk GaN microcavities, as supported by theoretical simulations.

Strong light-matter coupling in ultrathin double dielectric mirror GaN microcavities

Strong light-matter coupling is demonstrated at low temperature in an ultrathin GaN microcavity fabricated using two silica/zirconia Bragg mirrors, in addition to a three-period epitaxial (Al,Ga)N mirror serving as an etch stop and assuring good quality of the overgrown GaN. The λ∕2 cavity is grown by molecular beam epitaxy on a Si substrate. Analysis of angle-resolved data reveal key features of the strong coupling regime in both reflectivity and transmission spectra at 5K: anticrossing with a normal mode splitting of 43±2 meV and 56±2meV for reflectivity and transmission, respectively, and narrowing of the lower polariton linewidth near resonance.

Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots

We used continuous wave photoluminescence (cw-PL) and time resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe/(Zn,Mn)Se system the holes are confined in the non-magnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn,Mn)Se matrix. On the other hand, in the (Zn,Mn)Te/ZnSe system, the holes are confined in the magnetic (Zn,Mn)Te QDs, while the electrons remain in the surrounding non-magnetic ZnSe matrix. The magnetic polaron formation energies in both systems were measured from the temporal red-shift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe/(Zn,Mn)Se system the magnetic polaron shows conventional behavior with decreasing with increasing temperature T and increasing magnetic field B. In contrast, in the (Zn,Mn)Te/ZnSe system has unconventional dependence on temperature T and magnetic field B; is weakly dependent on T as well as on B. We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.

Strong light-matter coupling in bulk GaN-microcavities with double dielectric mirrors fabricated by two different methods

Two routes for the fabrication of bulk GaN microcavities embedded between two dielectric mirrors are described, and the optical properties of the microcavities thus obtained are compared. In both cases, the GaN active layer is grown by molecular beam epitaxy on (111) Si, allowing use of selective etching to remove the substrate. In the first case, a three period Al0.2Ga0.8N/AlN Bragg mirror followed by a λ/2 GaN cavity are grown directly on the Si. In the second case, a crack-free 2 μm thick GaN layer is grown, and progressively thinned to a final thickness of λ. Both devices work in the strong coupling regime at low temperature, as evidenced by angle-dependent reflectivity or transmission experiments. However, strong light-matter coupling in emission at room temperature is observed only for the second one. This is related to the poor optoelectronic quality of the active layer of the first device, due to its growth only 250 nm above the Si substrate and its related high defect density. The reflectivity sp...

Fabrication and characterization of ultrathin double dielectric mirror GaN microcavities

The optical properties and fabrication of ultrathin GaN-based microcavities grown on silicon substrates are described. The epitaxial part of the optical cavities, consisting of a λ/2 GaN layer above a 3-period epitaxial Bragg mirror, is sandwiched between two silica/zirconia mirrors. At a suitable point in the fabrication process the silicon substrate was selectively removed using via holes. The cavity mode and excitonic resonance are observed by reflectivity at low and room temperature, demonstrating a quality factor of ~125. The dispersion of the modes and their linewidth is measured using angle-resolved reflectivity and successfully modelled using transfer matrix simulations.

Strong Light-Matter Coupling in GaN-Based Microcavities Grown on Silicon Substrates

We present an overview of our work concerning the fabrication of GaN-based microcavities grown on silicon substrates dedicated to the observation of the strong light-matter coupling regime. In the view of recent promising results in the field, prospects regarding the improvement of heterostructures in order to observe room temperature polariton lasing from a GaN-based microcavity grown on a silicon substrate will be discussed.

Room temperature Strong coupling in low finesse GaN microcavities

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