Well-width dependence of exciton-longitudinal-optical-phonon coupling in MgZnO/ZnO single quantum wells

The well-width dependence of the exciton-phonon interaction in Mg(0.1)Zn(0.9)O/ZnO single quantum wells (QWs) with a wedged structure was investigated by photoluminescence (PL) measurements at 4 K. Within the Frank-Condon approximation, the Huang-Rhys factor S, as a measure of the coupling strength between the exciton and the longitudinal-optical (LO) phonon, was extracted from the relative intensities between the first-order phonon replica and the zero-phonon peak. It was found that the value of S increased monotonically with the increase of the well width (LW). By studying the excitation-density-dependent PL spectra, this result was successfully explained by taking into account the internal electric field originating from the spontaneous and piezoelectric polarizations. The electric field is expected to push electrons and holes to the opposite sides in the well, and consequently results in the increase of S with increasing LW.