Electrical and structural properties of rapidly annealed Pd/Mo Schottky contacts on n-type GaN

Electrical and structural properties of palladium/molybdenum (Pd/Mo) Schottky contacts on n-type GaN have been investigated as a function of annealing temperature by current-voltage (I-V), capacitance-voltage (C-V), x-ray diffraction (XRD) and Auger electron spectroscopy (AES) techniques. An as-deposited Pd/Mo/n-GaN Schottky diode exhibits a barrier height of 0.68 eV (I-V) and 0.82 eV (C-V), which increased to 0.75 eV (I-V) and 0.89 eV (C-V) after annealing at 400°C. However, it is noted that the barrier height slightly decreased to 0.73 eV (I-V) and 0.87 eV (C-V) when the contact was annealed at 500°C. A maximum barrier height of 0.78 (I-V) and 1.09 eV (C-V) was achieved on the Pd/Mo contacts annealed at 600°C. The Norde method was also employed to extract the barrier height of Pd/Mo contacts, and the values are 0.70 eV for the as-deposited and 0.82 eV for the contact annealed at 600°C which are in good agreement with those obtained by the I-V technique. Based on the Auger electron spectroscopy and x-ray diffraction studies, the formation of gallide phases at the Pd/Mo/n-GaN interface could be the reason for the increase of Schottky barrier heights upon annealing at elevated temperatures. The AFM results showed that there was no significant degradation in the surface morphology (rms roughness of 4.61 nm) of the contact even after annealing at 600°C. These results make Pd/Mo Schottky contacts attractive for high-temperature device applications.