  Infrared detection and sensing is deeply embedded in modern technology and
human society and its development has always been benefitting from the
discovery of new photoelectric response materials. The rise of two-dimensional
(2D) materials, thanks to their distinct electronic structure, extreme
dimensional confinement and strong light-matter interactions, provides new
material platform for next-generation infrared photodetection. Ideal infrared
detectors should have fast respond, high sensitivity and air-stability, which
is rare to meet at the same time for all existing 2D materials, either
graphene, transition metal dichalcogenide or black phosphorous. Herein we
demonstrate a new infrared photodetector based on 2D Bi2O2Se crystals, whose
main characteristics are superb in the whole 2D family: high sensitivity of ~65
A/W at 1200 nm and ultrafast intrinsic photoresponse of ~1 ps at room
temperature. Such great performance is attributed to the suitable electronic
bandgap and high carrier mobility of 2D oxyselenide. With additional merits of
mass production, excellent stability and flexibility, 2D oxyselenide detectors
should open new avenues in highly-sensitive, high-speed, low-cost, flexible
infrared photodetection and imaging.
