RESEARCH ACTIVITY

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Fig. 1 Schottky junctions based on a layered PdCoO₂ and β-Ga₂O₃ for high-temperature operation.

(A) Energy band diagram of a metal-semiconductor interface with a Schottky barrier of ϕ_b. ϕ_m, work function of metal; χ_s, electron affinity of semiconductor; E_vac, vacuum level; E_F, Fermi energy; E_C, conduction band minimum; V, bias voltage. The electron is depicted as a red circle. (B) Typical current-voltage characteristic of Schottky junction showing the current rectification behavior under forward (on-state) or reverse (off-state) bias voltage. The saturation current density J_s is noted in red. (C) Temperature dependence of the saturation current density J_s with Schottky barrier heights of 1.0 eV (blue), 1.4 eV (green), and 1.8 eV (red) calculated by the thermionic emission model using the Richardson constant of β-Ga₂O₃, A** = 41.1 A/cm² (24). (D) Schematic image for the characterization of the PdCoO₂/−β-Ga₂O₃ Schottky junction. (E) HAADF-STEM image of the PdCoO₂/β-Ga₂O₃ interface. The crystal orientation is represented by arrows. (F) Enlarged image of the HAADF-STEM image of the PdCoO₂/β-Ga₂O₃ interface. The anisotropic Ψ_d-s orbital proposed for the conduction band of PdCoO₂ is schematically shown (20). Right: Corresponding crystal model. The alternating Pd⁺ and [CoO₂]⁻ charged layers are shown based on the nominal ionic charges in the bulk PdCoO₂. The actual charge state at the interface can be modified by electronic reconstruction with screening charges.