Inhomogeneous interface dipole effect at the Schottky junctions of PdCrO₂ on β-Ga₂O₃ $(2¯01)$ substrates

We report the lateral and vertical electrical conduction properties of PdCrO₂ thin films grown on insulating Al₂O₃ (001) and conducting β-Ga₂O₃$(2¯01)$ substrates. The c-axis oriented PdCrO₂ films on the both substrates showed metallic temperature dependence of in-plane resistivity down to 2 K. In PdCrO₂/β-Ga₂O₃ vertical devices, rectifying current density–voltage (J–V) characteristics revealed the formation of a Schottky barrier at the PdCrO₂/β-Ga₂O₃ interface. The Schottky barrier height (SBH) of 1.2–1.8 eV, evaluated by J–V characteristics, is significantly larger than 0.8 eV expected from the usual Mott–Schottky relation based on the electron affinity of β-Ga₂O₃ (4.0 eV) and the work function of PdCrO₂ (4.8 eV) determined by ultraviolet photoelectron spectroscopy. The enhanced SBH at the PdCrO₂/β-Ga₂O₃ interface indicates the existence of interface dipoles, as in the case of PdCoO₂/β-Ga₂O₃. Besides, we observed a large difference of the SBH between the J–V measurements (1.2–1.8 eV) and capacitance measurements (2.0–2.1 eV). While the SBH is definitely enhanced by the interface dipole effect, the level of enhancement at the PdCrO₂/β-Ga₂O₃ interface is rather inhomogeneous, different from that at the PdCoO₂/β-Ga₂O₃. In fact, two typical types of interfaces were found by a high-angle annular dark-field scanning transmission electron microscope, which would be the origin of the inhomogeneous SBH. Further understanding of the interface formation between delafossite oxides and β-Ga₂O₃$(2¯01)$ will improve the performance of Ga₂O₃ Schottky junctions as a power diode available at high temperatures.