Engineering energy bands in 0D–2D hybrid photodetectors: Cu-doped InP quantum dots on a type-III SnSe2/MoTe2 heterojunction

Two-dimensional (2D) self-driven photodetectors have emerged as a compelling area of research, offering advantages such as miniaturization, weak light detection, high photosensitivity, and low noise levels. However, current type-III 2D heterojunction photodetectors often suffer from low self-driven responsivity and medium I_light/I_dark ratios. In this work, a novel device architecture that addresses these challenges is constructed by incorporating Cu-doped InP/ZnSeS/ZnS core-shell quantum dots (QDs) onto a type-III SnSe₂/MoTe₂ 2D heterojunction. The strategically engineered energy band structure of the Cu-doped QDs facilitates carrier transport with SnSe₂/MoTe₂ to form back-to-back type-II and type-III band alignments. As a result, under 532 nm illumination, the hybrid device exhibits remarkable visible light self-driven performance metrics with the help of the photogating effect: an ultra-low dark current of 23 fA, with responsivity and external quantum efficiency enhanced to 459 mA W^-1 and 109%, respectively, surpassing theoretical values by fourfold compared to those of pure SnSe₂/MoTe₂, a low noise equivalent power (NEP) of 0.87 × 10^-2 pW Hz^-1/2, a realistic specific detectivity of 1.45 × 10¹¹ Jones, a large I_light/I_dark ratio of 10⁶ and a swift response time of 1.16 ms/1.14 ms with stable operation. These results demonstrate that energy band engineering of Cu-doped QDs can significantly enhance the performance of 2D type-III heterojunctions in the visible range, laying a foundation for future gate-tunable optoelectronic devices.