Lateral confinement and band mixing in ultrathin semiconductor quantum wells with steplike interfaces

We study theoretically the effects of lateral confinement on the electronic structure of strained ultrathin InAs/InP (001) quantum wells (QWs) with one-dimensional (wirelike) interface islands. We develop a theoretical approach allowing the efficient computational treatment of a large class of one-dimensional structures within the framework of the surface Green's-function matching formalism. Using the semiempirical sp(3)s* nearest-neighbor tight-binding model, we calculate the energies, spatial distributions, and orbital character of electronic states for islands oriented along the <010> and <110> directions. The presence of the interface steps gives rise to localized states and leads to a band-gap reduction and an increase of the splitting between heavy holes (HH) and light holes (LH). We observe significant changes in the orbital character of both localized and extended (QW) states, namely a large anisotropy of the in-plane p components in all subbands and an increase of the p(z) contribution to HH states. The valence-band structure depends strongly on the wire orientation. In <110>-oriented islands, the HH-LH mixing is significantly enhanced by the lateral potential, whereas in <010> structures there is no evidence for such enhancement. The observed effects influence the optical properties of the structures and may cause optical anisotropy, relax some of the selection rules, and enhance the oscillator strengths for both interband and intersubband transitions.