High-Electron-Mobility $\hbox {Ge/GeO}_{2}$ n-MOSFETs With Two-Step Oxidation

We propose a two-step oxidation with high-pressure oxidation and low-temperature oxygen annealing to form ideal Ge/GeO₂ stacks based on thermodynamic and kinetic control. The capacitance-voltage (C-V) characteristics of Ge/GeO₂ MISCAPs with two-step oxidation revealed significant improvements of electrical properties, and the interface states density (Dit) estimated with a low-temperature conductance method that was below 10¹¹ eV^-1 cm^-2 near the midgap. On the basis of our understanding of Ge oxidation, we demonstrated very high electron mobility in Ge n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) that exceeded the universal mobility in Si-MOSFETs. The peak electron mobility in Ge n-MOSFETs with the two-step oxidation was 1100 cm²/V · s in the Al/GeO₂/Ge stack. This was achieved by taking care of the Ge/GeO₂ channel interface. Since we clarified that mobility was still limited by the remaining extrinsic scattering sources, the present results promise much higher performance Ge complementary metal-oxide-semiconductor.