Monolayer 2H-phase MoS₂-based photodetectors exhibit high photon absorption but suffer from low photoresponse, which severely limits their applications in optoelectronic fields. The metallic 1T phase of MoS₂, while transporting carriers faster, shows negligible response to visible light, which limits its usage in photodetectors. Herein, we propose an ultrafast-response MoS₂-based photodetector having a channel that consists of a 2H-MoS₂ sensitizing monolayer on top of 1T@2H-MoS₂. The 1T@2H-MoS₂ layer has a thickness of several nanometers and is a mixture of metallic 1T-MoS₂ and semiconducting 2H-MoS₂, imparting metal-like properties to the photodetector. Compared with the monolayer 2H-MoS₂ photodetector, we observed a drastic increase in the photoresponse of the 2H-MoS₂/1T@2H-MoS₂ vertically stacked photodetector to a value of 1917 A W^-1. Owing to the presence of metallic 1T-MoS₂ within the metal-like 1T@2H-MoS₂, the performance of the 2H-MoS₂/1T@2H-MoS₂ vertically stacked photodetector is voltage bias-modulated with an external quantum efficiency (EQE) of up to 448,384% and a specific detectivity of up to ∼10¹¹ Jones. The higher carrier density and higher mobility of the 1T@2H-MoS₂ layer explain the better bias-modulated performance. In addition, the interface between 2H-MoS₂ and 1T@2H-MoS₂ ensures fewer dangling bonds and reduced lattice mismatching. Thus, this study presents an exclusive vertically stacked MoS₂-based photodetector that lays the foundation for the development of photodetectors exhibiting higher photoresponse.

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