The precursor was put with a 1.6 s pulse in boost mode, followed by N2 purge. A 0.1 s pulse of H2O was then introduced, followed by another 6.0 s N2 purge. This process was repeated 1860 times to achieve a 100 nm thickness of TiO2. After the ALD process, ITO was deposited using physical vapor deposition (PVD) with a radio frequency (RF) sputtering technique. The Cu2O modified with Ga2O3 and TiO2 was placed in the PVD chamber (PVD Products Inc.), which was evacuated to below 8.5 × 10 -7 Torr. ITO deposition was conducted under the following conditions: 60 W RF power, 10 mTorr chamber pressure, 50 sccm Ar flow, and 30 rpm stage rotation without any heating process. The deposition was performed for 42 min to obtain a 150 nm ITO layer. The thickness of each layer was measured on a Si substrate using an alpha-SE ellipsometer (J.A. Woollam Co.).