Elementary theory of heterojunctions

An LCAO theory of heterojunction band-edge discontinuities is formulated and tested for approximate self-consistency. It leads to a table of valence-band maxima for all tetrahedral semiconductors; discontinuities can be obtained from the table directly by subtraction. The discrepancies with the current scattered data do not appear significantly larger than the uncertainty in those data, a few tenths of electron volts. A pseudopotential theory of such discontinuities is also formulated, based upon self-consistent atomic pseudopotentials. This leads to valence-band maxima reasonably consistent with the LCAO theory, except for junctions between materials of significantly different bond length. It also suggests that the Frensley—Kroemer scheme does produce self-consistency for systems of matching lattice constant, but produces incorrect trends with mismatch in lattice constant. The goal in any case is taken to be a table of valence-band maxima. LCAO values seem a better standard than photoelectric thresholds, though a comparison of the two indicates them to be roughly consistent for treating junctions if both sides are homopolar or if both sides are polar.