Van der Waals Heterostructure Mid-Infrared Emitters with Electrically Controllable Polarization States and Spectral Characteristics

Moderninfrared (IR) microscopy, communication, and sensingsystemsdemand control of the spectral characteristics and polarization statesof light. Typically, these systems require the cascading of multiplefilters, polarization optics, and rotating components to manipulatelight, inevitably increasing their sizes and complexities. Here, wereport two-terminal mid-infrared (mid-IR) emitters, in which tuningthe polarity of the applied bias can switch their emission peak wavelengthsand linear polarization states along two orthogonal orientations.Our devices are composed of two back-to-back p-n junctionsformed by stacking anisotropic light-emitting materials, black phosphorusand black arsenic-phosphorus with MoS2. By controllingthe crystallographic orientations and engineering the band profileof heterostructures, the emissions of two junctions exhibit distinctspectral ranges and polarization directions; more importantly, thesetwo electroluminescence (EL) units can be independently activated,depending on the polarity of the applied bias. Furthermore, we showthat when operating our emitter under the polarity-switched pulsemode, the time-averaged EL exhibits the characteristics of broad spectralcoverage, encompassing the entire first mid-IR atmospheric window(lambda: 3-5 mu m), and electrically tunable spectralshapes.