Effects of thermal annealing on the electrical and structural properties of Pt/Mo Schottky contacts on n-type GaN

Thermal annealing temperature effects on the electrical and structural properties of platinum/molybdenum (Pt/Mo) Schottky contacts on n-type GaN have been investigated by current-voltage (I-V), capacitance-voltage (C-V), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. As-deposited Pt/Mo/n-GaN Schottky diode exhibits barrier height of 0.75 eV (I-V) and 0.82 eV (C-V). Upon annealing at 400 and 500 A degrees C, the barrier height slightly increased to 0.77 eV (I-V) and 0.92 eV (C-V) and 0.82 eV (I-V) and 0.97 eV (C-V), respectively. A maximum barrier height of 0.83 eV (I-V) and 0.99 eV (C-V) is obtained on the Pt/Mo contacts annealed at 600 A degrees C. X-ray photoelectron spectroscopy results shows that the Ga 2p core-level shift towards the low-energy side for the contact annealed at 600 A degrees C as compared to the as-deposited one. Based on the results of XPS and XRD studies, the formation of gallide phases at Pt/Mo/n-GaN interface could be the reason for the increase of Schottky barrier heights upon annealing at elevated temperatures. The atomic force microscopy (AFM) results showed that the Pt/Mo contact does not seriously suffer from thermal degradation during annealing even at 600 A degrees C (RMS roughness of 5.41 nm). These results make Pt/Mo Schottky contacts attractive for high temperature device applications.