Coupling of ultrathin InAs layers as a tool for band-offset determination

Abstract

We have experimentally determined the band offsets at a highly strained InAs/GaAs interface by means of coupling between two ultrathin InAs layers embedded in a GaAs matrix. When both InAs layers are separated by a 32-ML barrier, the confined electron and light-hole (lh) states are split into symmetric and antisymmetric states, whereas the heavy-hole (hh) level is not split yet. Consequently, the splitting between the hh exciton transitions, which is measured by photoluminescence excitation spectroscopy, is solely determined by the conduction-band offset $\ensuremath{\Delta}{E}_{c}.$ Knowing $\ensuremath{\Delta}{E}_{c},$ the hh and lh band offsets $\ensuremath{\Delta}{E}_{\mathrm{hh}}$ and $\ensuremath{\Delta}{E}_{\mathrm{lh}}$ were subsequently determined from the coupling-induced shift and splitting in samples with 16-, 8-, and 4-ML barriers. We find a conduction-band offset of 535 meV, a conduction-band offset ratio of ${Q}_{c}=0.58,$ and a strain-induced splitting between the hh and lh levels of 160 meV. This method for the direct determination of band offsets is explicitly sensitive to the band-offset ratio, and its application is not restricted to particular type-I semiconductor heterostructures as long as the effective-mass--band-offset product for the conduction and valence bands differs by at least a factor of 2.