Spin-splitting of electron subbands in semiconducting films with a variable band gap

We investigate size-quantized electron states in a film (quantum well) with a variable band gap, based on compounds of Pb1−xSnxSe type. It is shown that an asymmetric modulation of the gap width in the direction of the growth of the film generally leads to spin-splitting of electron subbands. We discuss the influence of surface properties on the magnitude of the electron's spontaneous polarization. Finally, we point out some peculiar degeneracies of the spectrum, caused by particular boundary conditions.