Charged Versus Neutral Interfaces in III-V/Ge Quantum Wells

We discriminate between the charged and neutral character of Ge/III-V semiconductor interfaces by examining the band discontinuities across each interface in AlAs-Ge-GaAs(001) and GaAs-Ge-AlAs(001) single quantum well structures as a function of Ge thickness in the 2-16 monolayer range and comparing them with those of individual, isolated Ge-GaAs(001), Ge-AlAs(001), GaAs-Ge(001) and AlAs-Ge(001) heterojunctions. All structures were grown by molecular beam epitaxy at 360-degrees-C and examined in situ by X-ray photoemission spectroscopy. While ideally abrupt polar heterovalent interfaces are predicted to be charged, we find that all of the observed deviations from the commutativity and transitivity rules of heterojunction band offsets are consistent with the establishment of inequivalent, neutral IV/III-V and III-V/IV interfaces.