Polariton propagation in shallow-confinement heterostructures: Microscopic theory and experiment showing the breakdown of the dead-layer concept

Abstract

Polariton effects due to the interplay of the excitonic polarization of a semiconductor and a propagating light field are studied for transmission spectra of $\mathrm{Zn}\mathrm{Se}∕\mathrm{Zn}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ heterostructures. Calculations in terms of microscopic boundary conditions for the exciton motion within a finite-height confinement potential can explain the measured transmission spectra. These calculations also show the absence of polarization-free regions near the sample interfaces. Macroscopic models based on Pekar's additional boundary conditions can only reproduce the spectra if the band alignment at the $\mathrm{Zn}\mathrm{Se}∕\mathrm{Zn}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ interfaces is modified in comparison to the microscopic calculation and if a sample thickness is used that exceeds the independently determined experimental value. Our findings demonstrate the breakdown of the dead-layer concept for shallow confinement potentials.