Low Contact Resistance Ohmic Junctions in GaN Nanowire Devices by Rapid Thermal Annealing

GaN nanowires grown by a thermal evaporation method using Au nanoparticles as catalysts on silicon or alumna substrates have been studied. The wires have typical diameter $\sim $ 10-40 nm and are 5-10 $\mu $m in length. The growth proceeds by the VLS mechanism. Electrical contacts (Ti/Au) to the wires on Si/SiO2 substrates were made by standard e-beam lithography, e-beam evaporation and lift-off procedures. The as-prepared devices usually exhibit I-V behavior consistent with Schottky barrier injection. However, using rapid thermal annealing (a few minutes) in vacuum at temperature in the range 450-600\r{ }C, we have been able to produce dramatically lower contact resistance and linear I-V ohmic connections to our n-type GaN nanowires. Field-effect transistor (FET) and 4-probe resistivity characteristics of the devices are presented over the temperature range 10-300K and the data are discussed in terms of the electronic structure of the GaN nanowires.