Fig. 1. (Color online) Schematic illustration of the contact layer structure and c-TLM pattern used to measure contact resistance.

Fig. 2. (Color online) (a) The measured values of sheet resistance after annealing at various temperatures. (b) Comparison of the annealing temperature dependence of ρc between with and without the chemical surface treatment. (c, d) c-TLM-data examples for annealing temperature of 550 and 650 °C, respectively.

Fig. 3. (Color online) Comparison ofT_A-dependence of ρc between Ni 20 and Ni/Pd 2/60 contacts.

Fig. 4. (Color online) (a) Comparison of ρc–T_A relation among three samples listed inTable 1. (b) Simulated valence band curves near the contact depletion region for the three samples.

Fig. 5. (Color online) (a) STEM cross-sectional image of the sample C annealed at 550 °C. (b) EDX line analysis of Ga, In, Ni, Pd, Pt, and Au recorded along the blue arrow in Fig. 5(a).

Fig. 6. (Color online) The specific contact resistance ρc as a function of current density.

Table 1. Details of the structures of Ni/Pd-based metals and p-InGaN/p⁺-GaN contacting layers.