The Mechanism of Performance Variations in MoS2 Vertical Schottky Metal–Semiconductor Photodiode Based on Thermionic Emission Theory

Atomically thin 2-D semiconductors are widely used to build various novel photodiodes due to their appropriate band structure and dangling-bond-free surface. These emerging 2-D photodiodes have shown excellent performance, especially in responsivity. Here, we report a Schottky metal–semiconductor photodiode with an ultrashort molybdenum disulfide (MoS2) channel constructed by a vertical structure. The device showed excellent rectification and optical response characteristics due to the large Schottky barrier height (
$\text{q}\varphi _{\text{SB}}$
) through the physical transfer method to get rid of the Fermi-level pinning effect. In addition, the vertical structure dramatically reduces the channel length to the atomic scale and efficiently collects excited carriers with little recombination loss. Furthermore, the responsivity in those photodiodes is often associated with the light intensity and voltage bias. The thermionic emission theory was employed to explain the impacts of light intensity and voltage bias on the photodiode responsivity. This work can not only improve our fundamental understanding of the photovoltaic and photoconductive effects of 2-D semiconductors but also serve as an important reference for comparing and analyzing photodetectors based on 2-D semiconductors.