Metal-insulator transition of SrIrO₃ thin film by SrTiO₃ capping layer

When a SrIrO₃ thin film is deposited on a SrTiO₃ substrate using the PLD (Pulsed Laser Deposition) method, the temperature-dependent resistivity behavior is 'insulator-like', 'metal-like', or 'intermediate' depending on the deposition conditions. This is because the tilting angle of the Ir octahedron changes depending on the deposition conditions. When the SrIrO₃ thin film exceeds a certain thickness, its resistivity is small and its temperature-dependent resistivity behavior is insulator-like. However, if the thickness is small, the resistivity increases significantly and it becomes an insulator. Here we growth a SrTiO₃ capping layer on top of this SrIrO₃ thin film. When the thickness of the SrIrO₃ layer is large, there is no change due to the capping layer. However, when the thickness of the SrIrO₃ layer is small, the resistivity is greatly lowered due to the capping layer and shows metal-like resistance behavior. To investigate this more precisely, we systematically investigated the temperature-dependent resistivity behavior according to the thickness change of SrIrO₃. The thickness of the SrTiO₃ capping layer was fixed, and the resistivity was measured by varying the thickness of the SrIrO₃ thin film. When the thickness of SrIrO₃ is 9 to 20 unit cells, it showed insulator-like behavior. When it was 7 to 8 unit cells, it showed intermediate behavior. And when it was 1 to 6 unit cells, it showed metal-like behavior. Additionally, the “metal-like” SrIrO₃ thin film was not changed by the SrTiO₃ capping layer. We aim to determine the effect of SrTiO₃ capping layer on changing the resistivity of SrIrO3 thin films.