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Physical Interpretation of the Band Alignment

The significance of the effective-mass theorem to heterostructures is that it provides a precise definition of the idea of a ``position-dependent band edge.'' On the surface, it would seem that an attempt to describe a band-edge energy as a function of position would violate the uncertainty principle, because the states which lie at the band edge are momentum eigenstates. There is, however, no conflict in the idea of a position-dependent potential, so the local band-edge energy should really be interpreted as that potential which appears in the appropriate effective-mass Schrödinger equation for a given heterostructure. The reason for the indirectness of experimental measurements of the band alignment is now apparent: The band discontinuities are not directly observable quantities, but rather parameters (albeit essential ones) of a particular level of theoretical abstraction.



William R. Frensley
Sun May 21 16:29:20 CDT 1995