The role of interface states in the low temperature mobility of hafnium-oxide gated Ge-pMOSFETs and the effect of a hydrogen anneal

The interface state density has been measured as a function of bandgap energy for high-k gated germanium nMOS capacitors, using the high-low capacitance and conductance techniques. Effective mobility has been measured at 4.2 K on the corresponding pMOSFETs, which have a range of Ge/gate dielectric interface state densities, and modelled by assuming interface roughness and interface charge scattering at the SiO₂ interlayer/Ge interface dominate the mobility. A good correlation between measured interface state density and modelled charged impurity density is observed for these devices. A hydrogen anneal reduces the interface state density, as measured for capacitors and MOSFETs, with a corresponding decrease in the impurity sheet density fitting parameter in the latter. In addition, the hydrogen anneal results in a 20% reduction in the deduced interface root mean square (RMS) roughness.