Comparison of strong coupling regimes in bulk GaAs, GaN, and ZnO semiconductor microcavities

Wide band-gap semiconductors are attractive candidates for polariton-based devices operating at room temperature. We present numerical simulations of reflectivity, transmission, and absorption spectra of bulk GaAs, GaN, and ZnO microcavities in order to compare the particularities of the strong coupling regime in each system. Indeed the intrinsic properties of the excitons in these materials result in a different hierarchy of energies among the valence-band splitting, the effective Rydberg, and the Rabi energy, defining the characteristics of the exciton-polariton states independent of the quality factor of the cavity. Knowledge of the composition of the polariton eigenstates is central to optimize such systems. We demonstrate that in ZnO bulk microcavities, only the lower polaritons are good eigenstates and all other resonances are damped, whereas upper polaritons can be properly defined in GaAs and GaN microcavities.

Figure 1

(Color online) Comparison of reflectivity (straight line) and transmission (dashed line) spectra simulations of GaAs, GaN, and ZnO $\lambda$ microcavities at zero detuning and normal incidence.

Figure 2

(Color online) Angle-resolved reflectivity spectra of $\lambda$ microcavities. The straight yellow line represents the states with the same wave vector.

Figure 3

(Color online) [(a)–(c)] Angle-resolved dispersion of eigenstates in $\lambda$ microcavities simulated with the quasiparticle model. This model provides the energies of the bright and dark eigenstates. The homogeneous broadening of each state is figured as error bar. Dashed lines indicate exciton and photon dispersions in the absence of coupling. [(d)–(f)] Expansion coefficients of the eigenstates for the angle corresponding to the zero detuning within the exciton-photon basis.

Figure 4

(Color online) [(a)–(c)] ZnO absorption coefficient showing the excitonic resonances indicated by dashed lines on the other panels. Reflectivity, transmission, and absorption spectra of a ZnO $\lambda$ cavity calculated if the continuum is [(d)–(f)] taken into account or [(g)–(i)] not.

Figure 5

(Color online) Reflectivity spectra of a ZnO $\lambda$ microcavity when varying the inhomogeneous broadening: (a) $\sigma =1$, (b) 5, and (c) 30 meV.