High-mobility ZnV_xO_y/ZnO conduction path in ZnO/V/ZnO multilayer structure

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.