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

Modern infrared (IR) microscopy, communication, and sensing systems demand control of the spectral characteristics and polarization states of light. Typically, these systems require the cascading of multiple filters, polarization optics, and rotating components to manipulate light, inevitably increasing their sizes and complexities. Here, we report two-terminal mid-infrared (mid-IR) emitters, in which tuning the polarity of the applied bias can switch their emission peak wavelengths and linear polarization states along two orthogonal orientations. Our devices are composed of two back-to-back p-n junctions formed by stacking anisotropic light-emitting materials, black phosphorus and black arsenic-phosphorus with MoS2. By controlling the crystallographic orientations and engineering the band profile of heterostructures, the emissions of two junctions exhibit distinct spectral ranges and polarization directions; more importantly, these two electroluminescence (EL) units can be independently activated, depending on the polarity of the applied bias. Furthermore, we show that when operating our emitter under the polarity-switched pulse mode, the time-averaged EL exhibits the characteristics of broad spectral coverage, encompassing the entire first mid-IR atmospheric window (λ: 3-5 µm), and electrically tunable spectral shapes.

Van der Waals Heterostructure Photodetectors with Bias-Selectable Infrared Photoresponses.

A bias-selectable photodetector, which can sense the wavelength of interest by tuning the polarity of applied bias, is useful for target discrimination and identification applications. So far, those detectors are generally based on the back-to-back photodiode configuration via exploiting epitaxial semiconductors as optoelectronic materials, which inevitably lead to high fabrication costs and complex device architectures. Here, we demonstrate that our band-engineered van der Waals heterostructures can be applied as bias-selectable photodetectors. Our first prototypical device is mainly composed of black phosphorus (BP) and MoTe2 light absorbers sandwiching a thin MoS2 hole blocking layer. By varying the bias polarity, its spectral photoresponse can be switched between near-infrared and short-wave infrared bands, and our optoelectronic characterizations indicate that the detector can exhibit high external quantum efficiency (EQE) and fast operation speed. With this framework, we further demonstrate the detector with bias-selectable photoresponses within the mid-wave infrared band using BP/MoS2/arsenic-doped BP heterostructures and show that our developed detectors can be integrated into a single-pixel imaging system to capture dual-band infrared imaging.