Optimization of Ohmic Contacts to n-Type GaAs Nanowires

Group III–group 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 approximately 2×10−7Ωcm2 at room temperature, becoming an order of magnitude higher at T≃4.2 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 with various barrier shapes, but further insights into structural properties would require a full microscopic understanding of the complex diffusion processes.