Comparative study of Schottky diode characteristics in Ni, Ta and Ni/Ta metal contact schemes on n-GaN

We have reported current-voltage characteristics of Ta/- and Ni/Ta/n-GaN Schottky diodes under various thermal treatments. Experimental data indicate that the electrical characteristics of Ni/Ta diodes are controlled by the interracial properties of the Ta and GaN heterointerface for the as-deposited samples and strongly affected by the presence of an oxide layer (Ta₂O₅) in those high-temperature-annealed diodes. In regard to Ta/Ni diodes, probably because of thermal stability and wide-band-gap properties of tantalum oxide, dramatic improvement in Schottky diode performance was resulted after annealing at high temperatures. The corresponding barrier height and ideality factor values can reach 1.17 eV and 1.09, respectively, even at an annealing temperature of 800°C.