Schottky diodes of Ni/Au on n-GaN grown on sapphire and SiC substrates

GaN films were grown on sapphire and SiC substrates. The crystal qualities of GaN films were investigated by photoluminescence, atomic force microscopy, and electron-beam-induced current measurements, etc. It was found that the crystal quality of GaN on SiC is better than the one on sapphire. Ni/Au Schottky contacts were formed on the both samples. The electronic characteristics were obtained by current-voltage and capacitance-voltage measurements. Schottky diodes on sapphire substrate show breakdown voltage of -80 V. While for SiC substrate, the strong breakdown was not observed even at -100 V. The reverse leakage current of diodes based on SiC is over three orders of magnitude lower than that of sapphire substrate when the reverse voltage is above 50 V, which is due to the presence of low dislocation density and high thermal conductivity.