Gate-Controlled Polarity-Reversible Photodiodes with Ambipolar 2D Semiconductors

A photosensor with an amplitude-tunable and polarity-reversible response under gate modulation has potential as a computational photosensor, which can provide more recognition degree of data to enhance signal processing efficiency. Although, the ambipolar 2D semiconductors possess unique gate-tunable properties, the question of how to utilize this property to design polarity-reversible photodiodes for intelligent applications remains unanswered. Here, gate-controllable polarity-reversible photodiodes based on ambipolar 2D semiconductors with an asymmetrically metal-contacted architecture are proposed. By controlling the gate-field, the local carrier type and density profile can be manipulated in the channel due to the partial shielding feature of the asymmetrically metal-contacted architecture, resulting in a polarity-reversible photodiode. The reported WSe₂-based photodiode possesses excellent rectifying behavior with a rectification ratio over 10⁵, photovoltaic performance with 90% external quantum efficiency, and 2.3% power conversion efficiency under gate regulation. Meanwhile, the device exhibits reversible polarity of photovoltage from a negative to positive state under gate control. By utilizing the reversible photovoltage of the WSe₂ photodiode, an optoelectronic switch with a photovoltage polarity signal is demonstrated without a bias voltage. This photovoltage-reversible homodiode paves the way to develop 2D devices with multiple operation modes for potential applications in high-efficiency photovoltaics, intelligent vision sensors, and logic optoelectronics.