Bragg polaritons in a ZnSe-based unfolded microcavity at elevated temperatures

Abstract

In this contribution, we present strong coupling of ZnSe quantum well excitons to Bragg modes resulting in the formation of Bragg polariton eigenstates, characterized by a small effective mass in comparison to a conventional microcavity. We observe an anticrossing of the excitonic and the photonic component in our sample being a clear signature for the strong-coupling regime. The anticrossing is investigated by changing the detuning between the excitonic components and the Bragg mode. We find anticrossings between the first Bragg mode and the heavy- as well as light-hole exciton, respectively, resulting in three polariton branches. The observed Bragg-polariton branches are in good agreement with theoretical calculations. The strong indication for the existence of strong coupling is traceable up to a temperature of 200 K, with a Rabi-splitting energy of 24 meV and 13 meV for the Bragg mode with the heavy- and light-hole exciton, respectively. These findings demonstrate the advantages of this sample configuration for ZnSe-based devices for the strong coupling regime.

Influence of the sample design on the strong light-matter coupling in ZnSe-based periodic structures

“…Besides the increasing spectral width of the excitonic components with growing temperature the spectral shift of the emission attributed to the LBP shows a decrement for increasing temperatures. This is due to the anticrossing of the Bragg mode with the X hh , which we have already reported to occur at T = 130 K [10]. For temperatures exceeding 200 K the strong-coupling regime is broken due to the spectral broadening of the excitonic components.…”

“…This classification is underscored by the PL spectrum showing a dominant contribution of the ZnSe QW X hh together with a signature probably due to trionic recombination on the low-energy side. We have already shown earlier that the implementation of the QWs into the DBR structure results in the interaction of the first Bragg mode with the X hh and X lh states leading to the formation of three polariton states, the lower (LBP), middle (MBP) and upper Bragg-polariton (UBP) branch [10]. The strong indication for the existence of strong coupling is traceable up to a temperature of 200 K with Rabi-splitting energies of 24 meV and 13 meV between the Bragg-polaritons.…”

Tunable Bragg polaritons and nonlinear emission from a hybrid metal-unfolded ZnSe-based microcavity

“…The adjustment of the spectral position of the BM and the QW emission is challenging in comparison to a conventional MC, since it can only be controlled in an indirect way during epitaxial growth. Nevertheless, with such a design of the Bragg structure an optimum overlap of the electric field of the first Bragg mode and the QWs can be achieved 26 . In order to tune the Bragg mode two modifications were applied to the sample.…”

“…The observed three branches of the Bragg polaritons are the result of the coupling of the first BM with and with the light-hole ( ) excitons. The uncoupled (2.817 eV) and (2.835 eV) resonances are also visible in the spectrum due to the inefficient coupling of the QW exciting transitions to the BM for the upper DBR layers 25 , 26 . In addition, a less pronounced reflectivity minimum at 2.851 eV can be detected which originates from the absorption of the first excited state .…”

“…However, the periodic arrangement of the excitonic resonances in a Bragg structure provides a maximum overlap between the exciton wave function and the photon mode 25 . From the technological point of view, such structures offer a reduced number of growth interfaces between epitaxial layers compared to a conventional MC structure which ensures a positive impact on the crystal quality of the sample 25 , 26 .…”