Van der Waals contacted WSe₂ ambipolar transistor for in-sensor computing

Image sensors with an in-sensor computing architecture have shown great potential in meeting the energy-efficient requirements of emergent data-intensive applications, where images are processed within the photodiode arrays. It demands the composed photodiodes are reconfigurable, which are usually achieved by ambipolar two-dimensional (2D) semiconductors. To improve the ambipolar charges injection, here we report a top-gated field-effect transistor (FET) design that is of bottom van der Waals contact via transferring ambipolar 2D WSe₂ onto Pd/Cr source/drain electrodes. The devices exhibit nearly negligible effective barrier heights for both holes and electrons based on thermionic emission mode, and show an almost balanced on/off ratio in the p-branch and n-branch. By replacing the top gate with two aligned semi-gates, the devices can effectively function as reconfigurable photodiodes. They can be switched between PIN and NIP configurations via controlling the two semi-gates, exhibiting good linearity in terms of short-circuit current (I_SC) and incident light power density. The photodiode arrays are also demonstrated for in-sensor optoelectronic convolutional image processing, showing significant potential for in-sensor computing image processors.