Dielectric enhancement of excitons in near-surface quantum wells

The excitons in near-surface ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}/\mathrm{GaAs}$ QW's have been investigated by photoluminescence excitation and magnetophotoluminescence spectroscopy. The dielectric enhancement of excitons is demonstrated by measuring the splitting of the $2s$ and $1s$ excitons and the diamagnetic shift of the $1s$ exciton state. In agreement with theoretical calculations the exciton binding energy is found to be enhanced 1.5 times by the dielectric confinement for 5-nm-wide quantum wells with cap layer thicknesses below 3 nm.