Heterojunction band offsets and scaling

Abstract

It is shown that accurate x-ray photoemission spectroscopy values of the valence band offsets ΔEv for Ge/GaAs(110), GaAs/ZnSe(110), and Ge/ZnSe(110) vary linearly with the minimum band-gap difference and obey the simple scaling relation, ΔEv/ΔEg(min)=3/4. This empirical observation is compared with the predictions of current theories of heterojunction band lineups and the results are discussed. A theory relating average bulk crystal Hamiltonians to band offsets is developed and this theory is used to calculate band lineups in the tight-binding limit. It is shown that if only interactions between s and p orbitals on adjacent nearest-neighbor atoms are considered, the band lineups coincide with those predicted by Harrison and Tersoff [J. Vac. Sci. Technol. B 4, 1068 (1986)]. Since the latter do not satisfy the experimentally observed scaling relation, it is concluded that second nearest-neighbor contributions to ΔEv are important in the tight-binding limit.