High Density Germanium Nanowire Assemblies: Contact Challenges, Electrical Characterization and Photoconductivity Dynamics

The conductivity and photoconductivity properties of vertically aligned germanium nanowires, within anodised aluminium oxide (AAO) templates have been characterized by C-AFM and macro-contact measurements. Contact resistance between the nanowires and metal macro-contacts was minimized by polishing and gradual etching of the AAO surface, to expose the nanowires, prior to deposition of the contacts. Conductivity data from C-AFM and macro-contact measurements were found to be comparable suggesting that both methods are inherently suitable for evaluating the electrical transport properties of encapsulated nanowires within a matrix. Photoconductivity measurements indicate a photocurrent/dark current ratio of up to 40{\%} in the Ge nanowire matrix during illumination with an Ar laser between 457 -- 514 nm. These results are significant as the ability to make good ohmic contacts to nanowires, within well defined arrays, is key for the future `bottom-up' fabrication of multi-layered device architectures for future electronic and optoelectronic devices.