Fabrication of GaN-based nanoscale device structures utilizing focused ion beam induced Pt deposition

In this work we have demonstrated nanoscale GaN device structures made from individual GaN nanowires and electrical contacts utilizing focused ion beam (FIB) induced Pt deposition. These GaN nanowires were grown by direct reaction of Ga vapor with NH3 and had diameters ranging from 100nmto250nm and lengths up to 200μm. As-grown nanowires were dispersed on SiO2 coated p++ Si substrate. A 30keV Ga+ ion beam was used to dissociate (trimethyl)methylcyclopentadienyl-platinum precursor for depositing Pt contacts to GaN nanowires. FIB-deposited Pt contacts to GaN nanowires showed nonlinear I-V characteristics, which turned linear after annealing at 500°C for 30s in argon. Resistivity of a GaN nanowire measured using a four terminal contact geometry fabricated by depositing Pt with a FIB was in the range of 5×10−3Ωcm. Temperature dependent resistivity measurement of the GaN nanowire revealed semiconducting behavior with a weak temperature dependence of the resistivity. In this study both Ohmic and Schottky contacts to GaN nanowires have been realized with FIB-deposited Pt contacts. Barrier height and ideality factor have been extracted for the metal-GaN nanowire Schottky junctions, which had low reverse breakdown voltage and large ideality factor of 18. Modulation of the current through the nanowire was achieved by applying a bias to the Si substrate acting as a backgate. n-type depletion mode behavior was observed in the GaN nanotransistor, which was consistent with the impurity related background concentrations expected in this type of growth method. The heat generation during FIB deposition and the ion damage appeared to cause noticeable swelling of the nanowires under the Pt contacts. Electron beam induced Pt deposition was also used to fabricate electrical contacts to the nanowires.