Relaxation of hot excitons in inhomogeneously broadened ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ nanostructures

The dimensionality dependence of hot exciton relaxation was studied by means of photoluminescence (PL) spectroscopy comparing ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ quantum wells and quantum dots. In both systems, an efficient population of radiative excitonic ground states via longitudinal-optical (LO) phonon scattering is observed for an excess energy of the exciting laser corresponding to an integer number of LO-phonon energies. Thus, only selected areas of the inhomogeneously broadened systems contribute to the PL spectrum immediately after the exciting laser pulse. This results in a drastical reduction of the PL linewidth. In quantum wells, the redistribution of excitons occurs due to acoustic phonon assisted migration within the ${\mathrm{Cd}}_x{\mathrm{Zn}}_{1-x}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}$ layer. In contrast, this process is found to be substantially suppressed in quantum dots due to the three-dimensional exciton confinement.