Full-band envelope-function approach for type-II broken-gap superlattices

We present a charge self-consistent mesoscopic electronic-structure method for type-II broken-gap superlattices that is based on the multiband k ·p envelope-function method. This scheme avoids the separate classification and occupation of electron and hole states that causes the standard effective-mass theory to fail once conduction- and valence-band states strongly intermix. The computational efficiency of envelope-function methods is maintained. Free or bound charge-carrier redistributions can be taken into account self-consistently. With this method that we term as full-band envelope-function approach, we calculate effective band gaps, effective masses, and optical transition energies of InAs/GaSb superlattices as a function of the layer width. Good agreement with experiment is obtained. We also discuss semiconductor to semimetal transitions in wide layer structures. We find the charge carriers to form a two-dimensional gas of approximately massless Dirac particles at a critical layer width.