  We theoretically study electronic states in graded-gap junctions of IV-VI
compounds with band inversion. Using a two-band model within the ${\bf
k}\cdot{\bf p}$ approximation and assuming that the gap and the gap centre
present linear profiles, we demonstrate the existence of a set of localized
states along the growth direction with a discrete energy spectrum. The envelope
functions are found to be combination of harmonic oscillator eigenfunctions,
and the corresponding energy levels are proportional to the square root of the
quantum number. The level spacing can be directly controlled by varying the
structure thickness.
