Semimetal-semiconductor transition in InAs [sbnd]GaSb heterostructures

Abstract

In a heterostructure consisting of neighboring layers of InAs and GaSb in a large band-gap host like AlSb, the bottom of the InAs conduction band lies ∼150meV below the top of the GaSb valence band. However, because the electron and hole subbands are weakly coupled for non-zero values of the wavevector k ∥ along the layer, an anticrossing of the levels occurs at k ∥ = k c, where k 2 c = (2μ/ħ 2) (Δ−ε v 0−ε c 0). Here Δ is the band overlap, ε c 0 and ε v 0 are the lowest electron and hole subband energies, and μ is the reduced mass. The splitting is in the order of 5–10 meV. For an intrinsic material, the Fermi level lies in this gap, so that no semimetallic state occurs. If the InAs layers are sufficiently wide, or if an electric field can be applied across the heterostructure (by fabricating front and back gates) it is possible to have the first excited electron subband ε c 1 realize an anticrossing with ε v 0 as well. Then a true semimetallic state can occur with a circle of electrons in the ε c 1 subband near k ∥ = 0, and a ring of holes near the anticrossing in the hybridized valence subband. A semimetal-to-semiconductor transition should occur, which is driven by shifting the single-particle subband energies with an applied electric or magnetic field.