Passivation of the Ge/InP(110) interface by As interlayers: Interface reactions and band offsets

The formation of the Ge/InP(110) interface at room temperature and the influence of an additional arsenic interlayer on the interface chemistry, the film growth, and the electronic properties of this heterostructure have been investigated using core and valence level photoemission and low-energy electron diffraction. We have shown that an As interlayer at the Ge/InP(110) interface can completely suppress the interface reaction of the Ge with the substrate at room temperature, including partial In–Ge exchange and In segregation. The electronic situation at the interface is characterized by an anomalous evolution of the surface Fermi level with Ge coverage on InP(110) and a high valence band offset of ΔE v =1.01±0.07 eV , which is reduced to ΔE v =0.78±0.07 eV for Ge/As/InP(110). We may attribute the differences of the measured valence band offsets to a reaction-induced interface doping of the InP at the real Ge/InP(110) interface, which introduces an interface dipole layer. A calculation of this interface dipole contribution (0.38 eV) using the model of interface induced gap states gives a fair estimate for the experimentally observed difference of the valence band offsets.