Structural dipoles at interfaces between polar II-VI semiconductors CdS and CdTe and non-polar layered transition metal dichalcogenide semiconductors MoTe2 and WSe2

The electronic structure of heterojunctions between II-VI semiconductors (CdS, CdTe) and layered transition metal dichalcogenide semiconductors (MoTe2, WSe2) were investigated by soft x-ray photoelectron spectroscopy. The interfaces were formed sequentially by molecular beam epitaxy (MBE) of the II-VI semiconductors on van der Waals (0001)-surfaces of layered compound single crystals. The II-VI semiconductors grow with their polar hexagonal axis ([111] for CdTe, [0001] for CdS) parallel to the non-polar substrate [0001]-axis, without evidence for lattice distortions as prooved by TEM and LEED. Band offsets were determined from soft x-ray photoelectron spectra. Large substrate independent interface dipoles of 1.2 eV for CdS and 0.8 eV for CdTe were determined. The deviation of experimental band offsets from the electron affinity rule prediction is described by a simple model which takes the polarity of the grown interfaces into account.