Two-Dimensional Phototransistors with van der Waals Superstructure Contacts for High-Performance Photosensing

Semiconducting transition metal dichalcogenides (TMDs) possess exceptional photoelectronic properties, rendering them excellent channel materials for phototransistors and holding great promise for future optoelectronics. However, the attainment of high-performance photodetection has been impeded by challenges pertaining to electrical contact. To surmount this obstacle, we introduce a phototransistor architecture, in which the WS₂ channel is connected with an alternating WS₂-WSe₂ strip superstructure, strategically positioned alongside the source and drain contact regions. Illumination triggers efficient separation of photoexcited electrons and holes due to the type-II staggered band alignment within the superstructure. Consequently, the contact regions exhibit degenerately doped n⁺ WS₂ and p⁺ WSe₂ strips under light illumination, resulting in minimal contact resistivity with the metal electrodes. The resultant WS₂ phototransistor exhibits a remarkable responsivity of 2.4 × 10⁶ mA/W and an impressive detectivity of 2.6 × 10¹² Jones. Furthermore, our time-resolved measurements reveal the absence of persistent photoconductance. This proposed phototransistor architecture provides a route for high-performance photodetection, effectively surpassing previous limitations associated with electrical contact.