Polarity Control in Ge Nanowires by Electronic Surface Doping

The performance of nanoscale electronic and photonic devices critically depends on the size and geometry and may significantly differ from those of their bulk counterparts. Along with confinement effects, the inherently high surface-to-volume ratio of nanostructures causes their properties to strongly depend on the surface. With a high and almost symmetric electron and hole mobility, Ge is considered to be a key material extending device performances beyond the limits imposed by miniaturization. Nevertheless, the deleterious effects of charge trapping are still a severe limiting factor for applications of Ge-based nanoscale devices. In this work, we show exemplarily for Ge nanowires that controlling the surface trap population by electrostatic gating can be utilized for effective surface doping. The reproducible transition from hole- to electron-dominated transport is clearly demonstrated by the observation of electron-driven negative differential resistance and provides a significant step towards a better understanding of charge-trapping-induced transport in Ge nanostructures.