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

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Abstract
The interface properties of Al2O3-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 4×1011 state/cm2-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 cm2 using the tunnelling model of Preier, and about 1×10-18 cm2 using the surface potential fluctuation model of Nicollian and Goetzberger. With reactively sputtered Al2O3 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 cm2/V-sec and the gate threshold voltage is about 1 volt or less.