Subbands in the gap in inverted-band semiconductor quantum wells.

We calculate the states associated with layered structures composed of semiconductors of opposite band-edge symmetry within the two-band k\ensuremath{\cdot}p model. Interface states are present whenever the two gaps overlap. These are three-dimensional analogues of soliton states for which fractional charge character has been claimed. For a single interface there is a gapless pair of particlelike and holelike bands. A gap develops for quantum wells, whose magnitude varies with the well width. This system may be realizable using IV-VI semiconductor alloys.