ELEMENTARY CALCULATION OF THE BRANCH-POINT ENERGY IN THE CONTINUUM OFINTERFACE-INDUCED GAP STATES

The band alignment at ideal semiconductor interfaces may be described by the continuum of interface-induced gap states. These intrinsic inte rface states derive from the victual gnp states (ViGS) of the complex semiconductor band structure. The energy at which their character chan ges from predominantly donorlike to acceptor-like is defined as their branch point. This branch point is located slightly below the middle o f its band gap al the mean-value point in the Brillouin zone. By compa rison with GW band-structure data it is demonstrated that, first, the width of the band gap at the mean-value point equals the dielectric ba nd gap and that, second, the empirical tight-binding approximation rep roduces the dispersion of the GW valence bands from the middle to the mean-value point of the Brillouin zone. Branch points computed by Ters off for 15 semiconductors are found slightly below the middle of the r espective dielectric band gaps at the mean-value point of the Brilloui n zone, These results make possible simple calculations of branch poin ts for other zincblende-structure semiconductors.