Pt/Au, Ni/Au, Ni/Pt/Au Schottky contacts were placed on a quaternary Al0.84In0.13Ga0.03N epilayer. The electrical and structural properties of the as-deposited Pt/Au, Ni/Au, Ni/Pt/Au and annealed Ni/Pt/Au Schottky contacts were investigated as a function of annealing temperature using current-voltage (I-V), capacitance-voltage (C-V), and high resolution x-ray diffraction measurements (HR-XRD). According to the I-V, Norde, and C-V methods, the highest Schottky barrier height (SBH) was obtained for the Pt/Au (0.82eV (I-V), 0.83eV (Norde), and 1.09eV (C-V)) contacts when they were compared with the other as-deposited Schottky contacts. The estimated SBH of the annealed Ni/Pt/Au Schottky contacts, calculated from the I-V results, were 0.80eV, 0.79eV, and 0.78eV at 300 degrees C, 400 degrees C, and 500 degrees C, respectively. The SBH decreases with an increase in the annealing temperature up to 500 degrees C compared with that of the as-deposited Ni/Pt/Au Schottky contact. The observed extra peaks in the annealed samples confirm the formation of a new interfacial phase at the interface. However, the diffraction patterns of the annealed Schottky contacts did not change as a function of the annealing temperature. The higher ideality factors values were obtained for as-deposited Pt/Au (5.69), Ni/Au (6.09), and Ni/Pt/Au (6.42) Schottky contacts and annealed Ni/Pt/Au (6.42) Schottky contacts at 300 degrees C (6.89), 400 degrees C (7.43), and 500 degrees C (8.04). The higher n results can be attributed to current-transport mechanisms other than thermionic emission, such as dislocation related tunneling.