  Light-emitting diodes (LEDs) based on III-V/II-VI materials have delivered a
compelling performance in the mid-infrared (mid-IR) region, which enabled
wide-ranging applications, including environmental monitoring, defense and
medical diagnostics. Continued efforts are underway to realize on-chip sensors
via heterogeneous integration of mid-IR emitters on a silicon photonic chip.
But the uptake of such approach is limited by the high costs and interfacial
strains, associated with the process of heterogeneous integrations. Here, the
black phosphorus (BP)-based van der Waals (vdW) heterostructures are exploited
as room temperature LEDs. The demonstrated devices can emit linearly polarized
light, and their spectra cover the technologically important mid-IR atmospheric
window (3-4 um). Additionally, the BP LEDs exhibit fast modulation speed as
well as exceptional stability, and its peak extrinsic quantum efficiency
(QE~0.9%) is comparable to the III-V/II-VI mid-IR LEDs. By leveraging the
integrability of vdW heterostructures, we further demonstrate a silicon
photonic waveguide-integrated BP LED. The reported hybrid platform holds great
promise for mid-IR silicon photonics.
