Evidence of extreme type-III band offset at buried n -type CdO/p -type SnTe interfaces

At covalent semiconductor interfaces, the band alignment is determined by the location of the band edges with respect to the charge neutrality level, but extension of this method to more ionic semiconductor systems requires further consideration. Using the charge neutrality level concept, a type-III (or broken band gap) band offset is predicted at the interface between n-type CdO and p-type SnTe. Employing hard x-ray photoelectron spectroscopy, we report on the chemical composition at the buried interface and the valence-band offset. Chemical intermixing at the interface between SnTe and CdO is found to be limited to ∼2.5 nm in our heterojunction samples. We measure a valence-band offset of 1.95(±0.15 eV) irrespective of the layer configuration. Once the degenerate hole doping of the SnTe is considered, the measured band-edge offset agrees with the type-III offset predicted from alignment of the band edges with respect to the charge neutrality level of the semiconductors.