The formation of the Ni/Al0.2Ga0.8N Schottky contacts has been investigated by x-ray photoelectron spectroscopy. In situ scanning tunneling microscopy was used in parallel to investigate the morphology of the Ni covered surface after the last deposition. In the same way, results are presented through two perspectives: the intensity of core-level signals which give information on the growth mode, and the core-level binding energy positions which assess changes in electronic and chemical properties as a function of Ni coverage. Ni deposition on Al0.2Ga0.8N substrates follows the Stranski–Krastanov growth mode. It is suggested that Ni preferably reacts with the contaminants at the surface rather than with the epilayer itself. The Schottky barrier formation is discussed in terms of unified defect and metal-induced gap states models.