Electronic states of ultrathin InAs/InP (001) quantum wells: A tight-binding study of the effects of band offset, strain, and intermixing

We investigate theoretically the electronic structure of strained ultrathin InAs/InP (001) quantum wells (QWs), using the semiempirical ${\mathrm{sp}}^3{d}^5{s}^{*}$ nearest-neighbors tight-binding model, the virtual crystal approximation, and the surface Green’s function matching method. The energies of the bound states and the optical transitions are calculated for QW widths from 1 to 4 monolayers and for valence band offsets varying from 0.2 to 0.9 eV. The dependence of the transition energies on strain is investigated. The intermixing effects are studied for (i) graded interfaces with a diffusion concentration profile and (ii) ${\mathrm{InAs}}_x{\mathrm{P}}_{1-x}/\mathrm{InP}$ QWs of varying composition with abrupt interfaces. The effect of strain on the transition energies is found to be small for thin wells, whereas the effect of intermixing is significant and cannot be neglected. Comparing the results with experimental data, we conclude that the electronic structure of ultrathin InAs/InP (001) QWs cannot be accurately described within the simple model of a rectangular QW. The effect of intermixing however is sufficient to explain the experimental results within a reasonable range of band offsets and structure parameters.