N-channel enhancement-depletion most by Ge inclusion at the interface

The inclusion of Ge at the Si-SiO₂ interface is known (1) to shift the threshold voltage of an N-channel MOST in the positive direction by a controlled amount, changing its operation from the normal depletion to the enhancement mode. The purpose of this paper is to describe the changes in the standard MOS technology which make feasible the manufacture of an enhancement-depletion, N-channel type circuit with a potential for high switching speeds. The results of measurements, carried out to characterize the interface properties of such modified structures, throw some light on the possible nature of this effect.