Ni/Pd-based ohmic contacts to p-GaN through p-InGaN/p-GaN contacting layers

Specific contact resistance ρc to p-GaN was measured for various structures of Ni/Pd-based metals and thin(20–30 nm thick) p-InGaN/p+-GaN contacting layers. The effects of surface chemical treatment and annealing temperature were examined. The optimal annealing temperature was determined to be 550 ℃, above which the sheet resistance of the samples degraded considerably, suggesting that undesirable alloying had occurred. Pd-containing metal showed ～35% lower ρc compared to that of single Ni. Very thin(2–3.5 nm thick) p-InGaN contacting layers grown on 20–25 nm thick p+-GaN layers exhibited one to two orders of magnitude smaller values of ρc compared to that of p+-GaN without p-InGaN. The current density dependence of through this study was 4.9 × 10–5 Ω·cm2 @ J = 3.4 kA/cm2.