MoS₂ bipolar junction photo-transistor (BJPT) with high gain and millisecond speed

Semiconducting two-dimensional (2D) MoS₂ has emerged as a promising material for logic transistors and photodetectors, benefiting from its considerable mobility and strong light–mater interaction, along with the low cost and large area growth. However, the reported MoS₂ based photodiode and photoconductor suffer from either absence of gain or slow dynamic response, limiting their practical application with high sensitivity. Herein, the lateral bipolar junction photo-transistors (BJPT) with both PNP and NPN architectures are fabricated by partial chemical doping, which combine the advantages of both photodiode and photoconductor by producing a high photo-gain of ∼10³ electrons per photon adsorption due to the carrier amplification and remaining a well dynamic response with speed less than 10 ms. In this device, we achieve a high responsivity of 2 × 10³ A/W and high sensitivity with specific D^* up to 7.2 × 10¹¹ Jones at 635 nm in the amplification region. This work demonstrates a BJPT device scheme that can combine both high gain and fast temporal response in a single device, promoting the wide applications of 2D ultra-thin photodetectors.