Optical characterization of GaN/SiC heterojunctions andp-SiC has been performed to explain the current–voltage(I–V)characteristics in GaN/SiCn-pheterojunction diodes. TheI–Vcharacteristics exhibit tunneling-assisted current with low forward “turn-on” voltages around 1.15 V as opposed to the expected drift/diffusion current with a turn on around 2.5 V. Electroluminescence (EL) measurements on these diodes revealed an infrared peak at 1.25 eV and a red peak at 1.75 eV. Photoluminescence (PL) measurements onp-SiC yielded peaks at 1.25 and 1.80 eV. Since the band gap of 6H–SiC is 3.03 eV, we attribute the EL and PL peaks to radiative transitions from the conduction band edge to a defect level and subsequently down to the valence band edge ofp-SiC. This defect level is located 1.25 eV above the valence band edge. ©1998 American Institute of Physics.