Surface Chemistry and Electrical Properties of Germanium Nanowires

TL;DR

This study investigates the surface chemistry and electrical behavior of germanium nanowires, revealing how surface oxides and treatments influence device hysteresis and electrical properties, with implications for nanowire-based electronics.

Contribution

It provides new insights into the effects of surface chemistry, oxidation, and passivation on the electrical characteristics of germanium nanowires, including hysteresis reduction techniques.

Findings

Water molecules cause large hysteresis in GeNW FETs.

Vacuum annealing removes surface oxides and hysteresis.

High-k dielectric passivation improves surface stability.

Abstract

Germanium nanowires with p- and n-dopants were synthesized by chemical vapor deposition and used to construct complementary field effect transistors . Electrical transport and x-ray photoelectron spectroscopy data are correlated to glean the effects of Ge surface chemistry to the electrical characteristics of GeNWs. Large hysteresis due to water molecules strongly bound to GeO2 on GeNWs is revealed. Different oxidation behavior and hysteresis characteristics and opposite band bending due to Fermi level pinning by interface states between Ge and surface oxides are observed for p- and n-type GeNWs. Vacuum annealing above 400C is used to remove surface oxides and eliminate hysteresis in GeNW FETs. High-k dielectric HfO2 films grown on clean GeNW surfaces by atomic layer deposition (ALD) using an alkylamide precursor is effective serving as the first layer of surface passivation. Lastly, the depletion length along the radial direction of nanowires is evaluated. The result suggests that surface effects could be dominant over the bulk properties of small diameter wires.