Ultra‐Thin GeSe/WS₂ Vertical Heterojunction with Excellent Optoelectronic Performances

Abstract Heterostructural engineering of atomically thin 2D materials offers an exciting opportunity to fabricate atomically sharp interfaces for optoelectronic devices. Herein, GeSe/WS₂ heterojunction devices composed of 2D WS₂ (n‐type) and few‐layer GeSe (p‐type), are fabricated by transferring mechanically exfoliated GeSe to chemical vapor deposition (CVD)‐grown WS₂. Excellent rectification behavior is observed from the I−V characteristics of the GeSe/WS₂ heterojunction devices. The reverse photocurrent increases more rapidly than the forward photocurrent under a 635 nm laser illumination, indicating an effective separation of the photogenerated carriers under a minus bias. A large photocurrent on‐off ratio of 10³ at −5 V bias, a high responsivity (R_λ) of 1.1 A W⁻¹, a considerable specific detectivity (D*) of 1.3×10¹⁰ Jones, and a high external quantum efficiency (EQE) of 214.8%, are obtained. Owing to the large built‐in potential of the heterojunction, efficient charge transfer is achieved from the abrupt interfaces even though vastly different materials are used in the van der Waals (vdW) heterostructure. A convenient route is demonstrated for the preparation of ultra‐thin GeSe/WS₂ vdW heterojunctions. The results reveal great potential of the present GeSe/WS₂ vertical heterojunction for future applications in optoelectronics.