Interface Properties of Al₂O₃-Ge Structure and Characteristics of Al₂O₃-Ge MOS Transistors

Abstract

The interface properties of Al 2 O 3 -Ge structure formed on germanium wafers by DC reactive sputtering are evaluated. The fast interface states are diminished by subjecting the sample to heat treatment in an inert gas flow. The interface state density is estimated to be typically less than 4×10 11 state/cm 2 -eV from the shift of the flat-band voltage with temperature as originally adopted by Gray and Brown. From the measurement of the parallel conductance of the MOS structure, the electron capture cross section of the trap located at the interface is estimated to be about 0.9×10 -17 cm 2 using the tunnelling model of Preier, and about 1×10 -18 cm 2 using the surface potential fluctuation model of Nicollian and Goetzberger. With reactively sputtered Al 2 O 3 films as a gate insulator, n -channel germanium MOS transistors are made with a high effective mobility. The effective mobility is typically more than 2000 cm 2 /V-sec and the gate threshold voltage is about 1 volt or less.