Ambipolar to anti-ambipolar light-induced transition in WSe₂-based FETs

The growing need for efficient processing of large amounts of data in compact electronic systems is driving interest in investigating alternative device architectures. 2D material-based devices exhibiting anti-ambipolar behaviour represent a promising option to address this need. In this work, we investigate a WSe₂-based field-effect transistor that shows ambipolar conduction with dominant n-type behaviour in the dark. Under illumination, using either diffuse white LED light or a collimated red laser, the device exhibits a transition to anti-ambipolar transport, with a prominent current peak in a narrow driving voltage range, which is desirable for fast switching logic applications. This response allows for the identification, under controlled illumination conditions, of three distinct current levels in three different bias regions, which are suitable for implementing a three-state logic device. The peak amplitude varies linearly with light intensity, and the corresponding photodetection performance results in a significant responsivity of 0.13 A W^-1 under red laser illumination. The light-induced transition from ambipolar to anti-ambipolar behaviour is qualitatively described through energy band diagrams, with the photocurrent peak corresponding to the n-p transition point observed in the dark.