Exciton localization by a fractional monolayer of ZnTe inserted in a wide CdTe quantum well

We demonstrate experimentally and theoretically that excitons can be localized by an isoelectronic submonolayer insertion in a semiconductor quantum well. Fractional monolayers of highly strained ZnTe are inserted in a $\mathrm{CdTe}/{\mathrm{Cd}}_{1-x}{\mathrm{Mg}}_x\mathrm{Te}$ quantum well by molecular-beam epitaxy, leading to the localization of the light-hole excitons. This effect is due to the strain-induced potential created by the lattice mismatch between ZnTe and CdTe materials. The crossover between the heavy-hole exciton transition and the light-hole exciton transition is observed by changing the total amount of Zn deposited. The experimental results are consistent with the effective-mass calculations when the correction of the valence-band offset due to coupling with the spin-orbit and higher conduction bands is taken into account.