Gradient-Strained Van Der Waals Heterojunctions for High-Efficient Photodetectors
Maximizing light-to-electricity conversion efficiency is a crucial challenge for the practical applications of 2D material photodetectors. However, due to the lack of stable and precise electronic structure control methods for 2D materials, the driving force of photogenerated carriers is insufficient that severely hinders the efficiency of separation and transport. Herein, a gradient-modulated, stable and precise strain applied strategy for 2D materials is designed and constructed, which results in a significant improvement in the detect efficiency of ZnO/WSe 2 /graphene van der Waals heterojunction photodetectors. Different from the overall strain of all-component materials in typical photodetectors, biaxial tensile strain is applied to WSe 2 that can be precisely modulated by controlling the height of ZnO nanorods, while the strain is nearly unaffected to ZnO. As the strain modulation increases from 1.3% to 4.0%, the external quantum efficiency ( EQE ) of the heterojunction increases from 11.4% to 35.3%, representing a threefold increase. Furthermore, with increasing strain, the EQE can reach higher levels. Moreover, the strain-enhanced conversion efficiency mechanism is elucidated that results from the synergistic effect of the strain-induced WSe 2 exciton convergence and the strain-increased ZnO/WSe 2 interface barrier, which enhances the carrier interface separation efficiency.
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