Envelope Function Approximation (EFA) bandstructure calculations for III-Vnon-square stepped alloy quantum wells incorporating ultra-narrow (similarto 5 angstrom) epitaxial layers

We describe Envelope Function Approximation (EFA) bandstructure calculation s based on a 4-band electron (EL), heavy-hole (HH), light-hole (LH) and spl it-off hole (SO) effective mass Hamiltonian, with Burt-Foreman hermitianisa tion, which can handle III-V quantum well structures that incorporate ultra -narrow epi-layers. The model takes into account the coupling of EL, HH, LH and SO bands and is suitable for describing quantum wells tuned to the 1.0 - 1.55 mu m window exploited by optical fibre communication devices. We ha ve used the multi-band solver to calculate the bandstructure of an illustra tive InGaAsSb-AlGaSb non-square quantum well that incorporates 6 Angstrom p otential "spikes" in its well region. Calculations based on the Burt-Forema n hermitianised Hamiltonian and those based on a Hamiltonian with standard "symmetrised" hermitianisation are presented and compared. When coupling to the conduction band is excluded from the calculation, the latter formulati on leads to anomalous electron-like curvature of the dispersion curves for our spiked non-square quantum well structure.