  A long-wavelength infrared (IR) photodetector based on two-dimensional
materials working at room temperature would have wide applications in many
aspects in remote sensing, thermal imaging, biomedical optics, and medical
imaging. However, sub-bandgap light detection in graphene and black phosphorus
has been a long-standing scientific challenge because of low photoresponsivity,
instability in the air and highdark current. In this study, we report a highly
sensitive, air-stable and operable long-wavelength infrared photodetector at
room temperature based on PdSe2 phototransistors and its heterostructure. A
high photoresponsivity of ~42.1 AW-1 (at 10.6 {\mu}m) was demonstrated, which
is an order of magnitude higher than the current record of platinum diselenide.
Moreover, the dark current and noise power density were suppressed effectively
by fabricating a van der Waals heterostructure. This work fundamentally
contributes to establishing long-wavelength infrared detection by PdSe2 at the
forefront of long-IR two-dimensional-materials-based photonics.
