Optimization of ohmic contacts to n-type GaAs nanowires

TL;DR

This paper systematically studies ohmic contact formation to n-type GaAs nanowires, optimizing annealing parameters, measuring contact resistances, and modeling the effects of diffusion and Schottky barriers to improve electrical contacts for quantum device applications.

Contribution

It provides a set of optimal annealing parameters for Pd/Ge/Au contacts and a phenomenological model for contact resistance as a function of diffusion parameters.

Findings

Achieved low contact resistance of ~2×10^{-7} Ω·cm^2 at room temperature.

Reproducible contact resistance measurements and temperature dependence.

Numerical analysis of Schottky barrier influence on contact resistance.

Abstract

III-V nanowires are comprehensively studied because of their suitability for optoelectronic quantum technology applications. However, their small dimensions and the spatial separation of carriers from the wire surface render electrical contacting difficult. Systematically studying ohmic contact formation by diffusion to $n$-doped GaAs nanowires, we provide a set of optimal annealing parameters for Pd/Ge/Au ohmic contacts. We reproducibly achieve low specific contact resistances of $\sim2\times10^{-7}\,\Omega\text{cm}^2$ at room temperature becoming an order of magnitude higher at $T\simeq4.2\,$K. We provide a phenomenological model to describe contact resistances as a function of diffusion parameters. Implementing a transfer-matrix method, we numerically study the influence of the Schottky barrier on the contact resistance. Our results indicate that contact resistances can be predicted using various barrier shapes but further insights into structural properties would require a full microscopic understanding of the complex diffusion processes.