Electrical properties and interfacial reactions of rapidly annealed Ni/Ru Schottky rectifiers on n-type GaN

The effect of annealing temperature on the electrical and structural properties of Ni/Ru Schottky rectifiers have been investigated by current-voltage (I-V), capacitance-voltage (C-V), X-ray diffraction (XRD) and secondary ion mass spectrometer (SIMS) measurements. The measured Schottky barrier height for as-deposited Ni/Ru/n-GaN Schottky diode is 0.66 eV (I-V) and 0.79 eV (C-V). It is observed that the barrier height of the Ni/Ru Schottky contacts increases with an increase in annealing temperature. When the contact is annealed at 600 °C for 1 min in N₂ ambient, a maximum barrier height is achieved and the corresponding values are 0.79 eV (I-V) and 0.98 eV (C-V). It is observed that significant improvement in the electrical properties of Ni/Ru Schottky rectifier after annealing temperatures as compared to the as-deposited contact. Based on the results of SIMS and XRD, the formation of gallide phases at the Ni/Ru/n-GaN interface could be the reason for the increase of Schottky barrier height at elevated temperatures. Atomic force microscopy results showed that the surface morphology of the Ni/Ru Schottky contact is fairly smooth with a root-mean-square (RMS) roughness of 2.12 nm even after annealing at 600 °C. These results indicate that the Ni/Ru contacts could be attractive for high-temperature device applications.