Germanium nanowire transistors: A comparison of electrical contacts patterned by electron beam lithography and beam-assisted chemical vapour deposition

Abstract
Germanium (Ge) nanowires synthesized using the supercritical fluid-liquid-solid (SFLS) approach were assembled into single nanowire transistor device structures. After depositing the nanowires from solution onto an oxidized silicon substrate, they were electrically connected with source and drain electrodes using one of three approaches: electron beam lithography (EBL), focused ion-beam-(FIB)-assisted chemical vapour deposition, or focused electron-beam-(FEB)-assisted chemical vapour deposition. The electrical properties of the contacts varied greatly with the fabrication method used. Gold contacts patterned by EBL were plagued by high contact resistance with non-linear current-voltage behaviour and poor structural stability. Platinum metal contacts deposited by FEB and FIB were structurally stable with lower contact resistance. However, FIB damages the nanowire by ion milling, implantation, and amorphization. FEB on the other hand produces reliable ohmic electrical contact with minimal structural damage to the nanowire. Ge nanowires, surface-treated with isoprene or hexene prior to FEB device fabrication, exhibited the least resistive contacts with a total contact resistance of approximately 0.8 MΩ