Comparison of ohmic contact properties on n-GaN/p-SiC and n-AlGaN/p-SiC heterojunctions

GaN/SiC and Al 0.25Ga 0.75 N/SiC heterojunction diodes were fabricated using Al/Ti for p-ohmic contact to the SiC and Ti/Al/Pt/Au for n-ohmic contact to the GaN and AlGaN. Annealing at 850 °C for 20 s (GaN) or 120 s (AlGaN) was required for achieving specific contact resistances in the 10 −6 Ω cm 2 range. The reverse breakdown voltage showed a negative temperature coefficient in both types of sample, with value ∼5.5±2.5×10 −3 V/K. The I– V characteristics of both heterojunctions show evidence of tunneling via defect states.