Improved free-standing GaN Schottky diode characteristics using chemical mechanical polishing

Chemical mechanical polishing of free-standing GaN substrates is found to reduce the reverse leakage current of Ni/Au Schottky diodes fabricated on the Ga-face. The barrier height extracted from current-voltage measurements is found to increase from ∼0.4 eV on un-treated substrates to 0.75 eV on polished wafers, along with a reduction in diode ideality factor from 2 to 1.5. The electrical measurements are consistent with removal of a defective near-surface region that promotes generation-recombination current. More acidic polishing solutions were found to produce the best Schottky diode characteristics and there was an optimum loading force during CMP of the GaN surface.