Yttrium passivation of defects in GeO$_{2}$ and GeO$_{2}$/Ge interfaces

Abstract

Alloying amorphous GeO$_{2}$ with Y$_{2}$O$_{3}$ has been found experimentally to improve its chemical stability and electrical reliability as a gate dielectric in Ge-based field effect transistors. The mechanism is explained here based on density functional calculations. The GeO$_{2}$ reliability problem is correlated with oxygen deficiency defects, which generate gap states near the band-edges of the underlying Ge. These can be passivated through Y doping. This shifts the defect gap state out of the gap up into the GeO$_{2}$ conduction band, thus effectively passivating gap states in the GeO$_{2}$ layer.