Disorder effects in focused-ion-beam-deposited Pt contacts on GaN nanowires.

The current-bias (I-V) characteristics at various temperatures, T, of focused-ion-beam (FIB)-deposited Pt contacts on GaN nanowires evolves from low-resistance ohmic (linear I-V) to rectifying as the diameter increases, and both exhibit strongly nonmetallic T-dependence. The small-diameter (66 nm) T-dependent resistance is explained by two-dimensional variable range hopping with a small characteristic energy, ensuring low resistance at 300 K. For large diameters (184 nm), back-to-back Schottky barriers explain the nonlinear I-V at all T values and permit an estimate of doping concentration from the bias-dependent barrier height. Both behaviors can be understood by accounting for the role of FIB-induced amorphization of GaN underneath the contact, as confirmed by cross-sectional transmission electron microscopy.