4.5 SiGe heterojunctions and band offsets

When two semiconductors are joined at a heterojunction, discontinuities occur in the valence bands and in the conduction bands. For an atomically abrupt interface, these discontinuities are sharp on an atomic length scale (i.e. on the order of a few atomic distances). This is in contrast with band-bending effects, which are associated with depletion layers, and which occur on much larger length scales (hundreds of A, up to several Ilm). The band discontinuities actually enter as boundary conditions in the solution of Poisson's equation, which would produce the band bending.