EMPIRICAL TIGHT-BINDING CALCULATION OF THE BRANCH-POINT ENERGY OF THECONTINUUM OF INTERFACE-INDUCED GAP STATES

The band lineup at metal-semiconductor contacts as well as at semicond uctor heterostructures may be described by one and the same physical c oncept, the continuum of interface-induced gap states. These intrinsic interface states derive from the virtual gap states (ViGS) of the com plex semiconductor band structure and their character varies from pred ominantly donorlike closer to the valence band to mostly acceptorlike nearer to the conduction band. Calculations are presented of the respe ctive branch points for elemental and binary as well as ternary compou nd semiconductors which make use of Baldereschi's concept of mean-valu e points in the Brillouin zone [Phys. Rev. B 7, 5212 (1973)], Penn's i dea of dielectric band gaps [Phys. Rev. 128, 2093 (1962)], and the emp irical tight-binding approximation (ETB). The results are as follows. First, at the mean-value point the band gaps calculated in the GW appr oximation have the same widths as the dielectric band gaps. Second, th e ETB approximation reproduces the GW valence-band energies at the mea n-value point. Third, the branch points of the ViGS are slightly below midgap at the mean-value point. The ETB branch-point energies excelle ntly reproduce the barrier heights of gold Schottky contacts on 19 sem iconductors and the valence-band offsets of Al1-xGaxAs/GaAs heterostru ctures. (C) 1996 American Institute of Physics.