Control of Schottky barrier height in metal/β-Ga2O3 junctions by insertion of PdCoO2 layers

Control of Schottky barrier heights (SBHs) at metal/semiconductor interfaces is a critically important technique to design switching properties of semiconductor devices. In this study, we report the systematic variations of SBHs in metal/PdCoO2/beta-Ga2O3 junctions with an increase in the thickness of the PdCoO2 insertion layer. The PdCoO2 insertion layer consists of ionic Pd+ and [CoO2](-) sublattices alternatingly stacked along the normal of the Schottky interface. This polar layered structure of PdCoO2 spontaneously induces interface dipoles that increase the SBH in beta-Ga2O3 devices. We fabricated Schottky junctions composed of metal/PdCoO2/beta-Ga2O3 (-201) with the PdCoO2 thickness of 0-20 nm. With an increase in the PdCoO2 thickness, we observed a systematic shift of current density-voltage (J-V) characteristics to larger forward driving voltage. The shift of J-V characteristics indicates the enhancement of SBH by insertion of the PdCoO2 layer, which was confirmed by the capacitance measurement as the consistent shift of the built-in potential. These results demonstrate a controllable SBH in a wide range of 0.7-1.9 eV driven by a decisive contribution of the interface dipole effect. The Schottky junctions based on beta-Ga2O3 with variable barrier heights could fit a wide range of applications, with the significant merits of optimizable switching properties.