Hot exciton relaxation in coupled ultra-thin CdTe/ZnTe quantum well structures

TL;DR

This study investigates hot exciton relaxation in coupled CdTe/ZnTe quantum well structures, revealing how energy transfer and phonon emission influence photoluminescence spectra and exciton dynamics.

Contribution

It provides a detailed analysis of hot exciton relaxation mechanisms and models charge and energy transfer in asymmetric double quantum wells.

Findings

PL from shallow QW is dominated by hot exciton recombination at weak excitation.

The ratio of PL intensities decreases exponentially with initial exciton kinetic energy.

Energy relaxation involves LO phonon emission up to over 20 phonons above bandgap.

Abstract

The photoluminescence (PL) and PL excitation (PLE) spectra of CdTe/ZnTe asymmetric double quantum well (QW) structures are studied on a series of samples containing two CdTe layers with nominal thicknesses of 2 and 4 monolayers (ML) in the ZnTe matrix. The samples differ in the thickness of the ZnTe spacer between CdTe QWs which is 45, 65 and 75 ML. It has been found that at above-barrier excitation the PL from a shallow QW at sufficiently weak excitation intensities is determined by recombination of hot excitons. It is shown that under these conditions, when PL is excited by lasers with different wavelengths, the ratio of the PL intensities from shallow and deep QWs decreases exponentially with an increase of the initial kinetic energy of hot excitons. It is found that energy relaxation of hot excitons with LO phonon emission determine the shape of the PLE spectrum of shallow QW in the range of exciton kinetic energies up to more than 20 LO phonons above ZnTe bandgap. We have shown that the results obtained are well described by the model of charge and energy transfer between QWs.