Multiband coupling and electronic structure of (InAs)n/(GaSb)n superlattices

The electronic structure of abrupt (InAs)(n)/(GaSb)(n) superlattices is calculated using a plane wave pseudopotential method and the more approximate eight band k.p method. The k.p parameters are extracted from the pseudopotential band structures of the zinc-blende constituents near the Gamma point. We find, in general, good agreement between pseudopotencial results and k.p results, except as follows. (1) The eight band k.p significantly underestimates the electron confinement energies for n less than or equal to 20. (2) While the pseudopotential calculation exhibits (a) a zone center electron-heavy hole coupling manifested by band anticrossing at n=28, and (b) a light hole-heavy hole coupling and anticrossing around n=13, these features are absent in the kp model. (3) As k.p misses atomistic features, it does not distinguish the C-2v symmetry of a superlattice with no-common-atom such as InAs/GaSb from the D-2d symmetry of a superlattice that has a common atom, e.g., InAs/GaAs. Consequently, kp lacks the strong in-plane polarization anisotropy of the interband transition evident in the pseudopotential calculation. Since the pseudopotential band gap is larger than the k.p values, and most experimental band gaps are even smaller than the k.p band gap, we conclude that to understand the experimental results one must consider physical mechanisms beyond what is included here (e.g., interdiffusing, rough interfaces, and internal electric fields), rather than readjust the kp parameters. [S0163-1829(99)07531-1].