Electrical, structural and morphological characteristics of rapidly annealed Ni/Pd Schottky rectifiers on n-type GaN

Schottky rectifiers are fabricated on n-type GaN using Ni/Pd metallization scheme and its characteristics have been investigated by current-voltage (I-V), Capacitance-Voltage (C-V), X-Ray Diffraction (XRD) and SIMS measurements as a function of annealing temperature. The calculated Schottky barrier height of the as-deposited contact was found to be 0.60 eV (I-V), 0.71 eV (C-V) with an ideality factor of 1.44. However, the barrier height slightly increases after annealing at 300, 400 and 500 °C. On the basis of the experimental results, a high-quality Schottky contact with barrier height and ideality factor of 0.81 eV (I-V), 0.88 eV (C-V) and 1.13 respectively, can be obtained after annealing at 600 °C for 1 min in a nitrogen atmosphere. Further, after annealing at 700 °C, it is found that the barrier height slightly decreased to 0.74 eV (I-V) and 0.85 eV (C-V). From the above observations, one can note that Ni/Pd Schottky contact exhibits excellent electrical properties after a rapid thermal annealing at 600 °C. According to the SIMS and XRD analysis, the formation of gallide phases at the Ni/Pd/n-GaN interface could be the reason of the barrier height increase at elevated annealing temperatures. The Atomic Force Microscopy (AFM) results show that the overall surface morphology of Ni/Pd Schottky contacts on n-GaN is fairly smooth. The above observations reveal that Ni/Pd Schottky metallization scheme was a good choice for the fabrication of high-temperature and high-power device applications.