Zirconia-germanium interface photoemission spectroscopy using synchrotron radiation

An ultrathin zirconia gate dielectric had been successfully incorporated into germanium metal-oxide-semiconductor (MOS) devices demonstrating very high-permittivity gate stacks with no apparent interfacial layer. In this study, synchrotron-radiation photoemission spectroscopy has been applied on the same gate stack to identify and quantify the presence of any interfacial germanium suboxide layer. By taking progressive core-level spectra during the layer-by-layer removal of the zirconia film, an oxidized germanium layer with submonolayer thickness was found, possibly arising from an interfacial Zr–O–Ge bonding configuration. In addition, the offsets in the valence-band spectra were also monitored and the energy-band diagram of the zirconia–germanium heterostructure was constructed. Compared to high-κ gate stacks on Si, the thinner interfacial layer and larger conduction-band offset in high-κ gate stacks on Ge suggest better scalability towards an ultimately higher MOS gate capacitance.