We report on a simple passivation strategy to improve the device performance of a near infrared (NIR) photodetector. Optoelectronic analysis reveals that after ultrathin AlO_xpassivation, the device exhibits an obvious increase in on/off ratio. What is more, the response speed of the device was improved by more than 100 times, from 48 μs to 380 ns.

Advances in the photocurrent conversion of two-dimensional (2D) transition metal dichalcogenides have enabled the realization and application of ultrasensitive and broad-spectral photodetectors. The requirements of previous devices constantly drive for complex technological implementation, resulting in limits in scale and complexity. Furthermore, the development of large-area and low-cost photodetectors would be beneficial for applications. Therefore, we demonstrate a novel design of a heterojunction photodetector based on solution-processed ultrathin MoSe2 nanosheets to satisfy the requirements of its application. The photodetector exhibits a high sensitivity to visible–near infrared light, with a linear dynamic range over 124 decibels (dB), a detectivity of ~1.2 × 10¹² Jones, and noise current approaching 0.1 pA·Hz^–1/2 at zero bias. Significantly, the device shows an ultra-high response speed up to 30 ns with a 3-dB predicted bandwidth over 32 MHz, which is far better than that of most of the 2D nanostructured and solution-processable photodetectors reported thus far and is comparable to that of commercial Si photodetectors. Combining our results with material-preparation methods, together with the methodology of device fabrication presented herein, can provide a pathway for the large-area integration of low-cost, high-speed photodetectors.

Layer-by-layer stacked and oxygen-incorporated WS ₂ microrods that exhibit strong absorption in both the visible light region and the 1100–2000 nm NIR light region are synthesized and demonstrated as broadband, self-driven, fast-response photodetectors.

Photodetectors based on high-performance, two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) are limited by the synthesis of larger-area 2D TMDCs with high quality and optimized device structure. Herein, we report, for the first time, a uniform and stacked–layered MoSe ₂ film of high quality was deposited onto Si substrate by using the pulsed laser deposition technique, and then in situ constructed layered MoSe ₂ /Si 2D–3D vertical heterojunction. The resultant heterojunction showed a wide near-infrared response up to 1550 nm, with both ultra-high detectivity up to 1.4 × 10 ¹⁴ Jones and a response speed approaching 120 ns at zero bias, which are much better than most previous 2D TMDC-based photodetectors and are comparable to that of commercial Si photodiodes. The high performance of the layered MoSe ₂ /Si heterojunction can be attributed to be the high-quality stacked–layered MoSe ₂ film, the excellent rectifying behavior of the device and the n-n heterojunction structure. Moreover, the defect-enhanced near-infrared response was determined to be Se vacancies from the density functional theory (DFT) simulations. These results suggest great potential of the layered MoSe ₂ /Si 2D–3D heterojunctions in the field of communication light detection. More importantly, the in situ grown heterojunctions are expected to boost the development of other 2D TMDCs heterojunction-based optoelectronic devices.