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In this study, a 300 °C-annealed 3 × 4 V/ZnO multilayer structure demonstrates the lowest resistivity (3.82 × 10−3 Ω cm) and the highest mobility (18 cm2/V s) among the studied V/ZnO multilayer structures. By measuring the energy bandgap (Eg), work function (Φ), and electron affinity (χ) by ultraviolet photoelectron spectroscopy and photoluminescence analysis, the corresponding energy band diagram at the ZnVxOy/ZnO interface can be constructed. A potential is observed at the ZnVxOy/ZnO interface, which induces the two-dimensional electron gas (2DEG) effect, and this is attributed to the high-mobility conduction path. The potential well directly relates to the Φ difference between the ZnO and ZnVxOy layers, which is determined to be 0.22, 0.46, and −0.1 eV for the as-deposited, 300 °C-annealed, and 500 °C-annealed V/ZnO multilayer structures, respectively. The 300 °C-annealed V/ZnO multilayer structure could possibly have the largest depth in the potential well. This supports the 2DEG mechanism for the high mobility of the 300 °C-annealed V/ZnO multilayer structure.

This study reports a transparent p-type TiO2 thin film by DC reactive magnetron sputtering method with 10% O2 partial pressure. The p-type conduction of TiO2 thin film was also confirmed by Seebeck effect. The lowest resistivity (1.458×10-2 Ω·cm) of the studied TiO2 thin film occurs at the annealing temperature of 500 °C in the under N2 atmosphere ambient. We believe that the p-type conduction mechanism of the as-deposited TiO2 thin films with 10% O2 partial pressure could be caused by the defect reaction mechanism, i.e., the Ti2+-Ti4+ substitution reaction. A transparent p-n junction of p-TiO2/n-ITO was fabricated by photolithography and lift-off processes. The I-V curve of p-TiO2/n-ITO junction shows that p-TiO2/n-ITO p-n junction clearly exhibits a good diode characteristic with a turn-on voltage of about 3.19 V under forward-biased voltage, which corresponds to the band gap of the TiO2. It further proves that the current studied TiO2 thin film prepared with 10% O2 partial pressure is the p-type conduction.This study reports a transparent p-type TiO2 thin film by DC reactive magnetron sputtering method with 10% O2 partial pressure. The p-type conduction of TiO2 thin film was also confirmed by Seebeck effect. The lowest resistivity (1.458×10-2 Ω·cm) of the studied TiO2 thin film occurs at the annealing temperature of 500 °C in the under N2 atmosphere ambient. We believe that the p-type conduction mechanism of the as-deposited TiO2 thin films with 10% O2 partial pressure could be caused by the defect reaction mechanism, i.e., the Ti2+-Ti4+ substitution reaction. A transparent p-n junction of p-TiO2/n-ITO was fabricated by photolithography and lift-off processes. The I-V curve of p-TiO2/n-ITO junction shows that p-TiO2/n-ITO p-n junction clearly exhibits a good diode characteristic with a turn-on voltage of about 3.19 V under forward-biased voltage, which corresponds to the band gap of the TiO2. It further proves that the current studied TiO2 thin film prepared with 10% O2 partial pressure is the p-type conduc...