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 (0.82 eV (I–V), 0.83 eV (Norde), and 1.09 eV (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 0.80 eV, 0.79 eV, and 0.78 eV at 300°C, 400°C, and 500°C, respectively. The SBH decreases with an increase in the annealing temperature up to 500°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°C (6.89), 400°C (7.43), and 500°C (8.04). The higher n results can be attributed to current-transport mechanisms other than thermionic emission, such as dislocation related tunneling.