Direct comparison of plain and oxidized metal Schottky contacts on β-Ga2O3

High quality Ru, Ir, Pd, Pt, Ag, and Au Schottky contacts (SCs) were fabricated on 2 ¯ 01 β-Ga2O3 single crystal substrates via rf sputtering under inert and oxidizing plasma conditions. The oxidized SCs exhibited significantly higher rectifying barriers and, with the exception of gold oxide, significantly improved high temperature performance, with more than 12 orders of magnitude of stable rectification at 180 °C. With the exception of Ag, the image-force-corrected laterally homogeneous barrier heights of the plain metal SCs were pinned close to 1.3 eV, irrespective of the metal work function, with the Fermi level at the SC interface close to the predicted VO (2+/0) transition level of fourfold coordinated oxygen vacancies. The equivalent barrier heights of the oxidized SCs were consistently 0.5–0.8 eV higher than their plain metal counterparts, lying in the range of 1.8–2.5 eV, with the increase attributed to the passivation of interfacial oxygen vacancies and a significant increase in the work function of the oxidized metals. The highest Schottky barriers for both the plain and oxidized metal SCs involved Ag, which may be linked to the relative ease of its unintentional and intentional oxidation, respectively. The very high rectifying barriers and the thermal stability of oxidized Schottky contacts to β-Ga2O3 indicate their potential for high temperature device applications.