Silicon-Phosphorene Nanocavity-Enhanced Optical Emission at Telecommunications Wavelengths

Emerging 2D Materials and Van der Waals Heterostructures for Advanced NIR, SWIR, and MWIR Emitters

Infrared (IR) emitters have drawn considerable attention for applications in deep-tissue imaging, optical communication, and thermal sensing. While III-V and II-VI semiconductors are traditionally used in these emitters, their reliance on complex epitaxial growth to overcome lattice mismatch and thermal expansion challenges leads to intricate device structures and limits their integrability. In contrast, 2D materials provide a more flexible solution, offering diverse optical bandgaps and the ability to be vertically restacked in arbitrary crystal orientations to form complex van der Waals (vdW) heterostructures, which can be further integrated onto diverse device platforms. This review highlights recent advancements in 2D-based IR emitters, focusing on the NIR, SWIR, and MWIR regions. It discusses the photoluminescence properties of 2D materials and innovative vdW engineering techniques used to develop IR light-emitting diodes (LEDs). The review also explores how external stimuli, such as electric fields and strain, can enable tunable emission wavelengths and examines the integration of 2D-based emitters with photonic structures, like cavities and waveguides, to create hybrid photonic devices. Finally, the review addresses the challenges and prospects of 2D-based IR technologies, highlighting their potential to transform IR light sources across various applications.

Liquid-Phase Exfoliation of Magnetically and Optoelectronically Active Ruthenium Trichloride Nanosheets

α-RuCl₃ is a layered transition metal halide that possesses a range of exotic magnetic, optical, and electronic properties including fractional excitations indicative of a proximate Kitaev quantum spin liquid (QSL). While previous reports have explored these properties on idealized single crystals or mechanically exfoliated samples, the scalable production of α-RuCl₃ nanosheets has not yet been demonstrated. Here, we perform liquid-phase exfoliation (LPE) of α-RuCl₃ through an electrochemically assisted approach, which yields ultrathin, electron-doped α-RuCl₃ nanosheets that are then assembled into electrically conductive large-area thin films. The crystalline integrity of the α-RuCl₃ nanosheets following LPE is confirmed through a wide range of structural and chemical analyses. Moreover, the physical properties of the LPE α-RuCl₃ nanosheets are investigated through electrical, optical, and magnetic characterization methods, which reveal a structural phase transition at 230 K that is consistent with the onset of Kitaev paramagnetism in addition to an antiferromagnetic transition at 2.6 K. Intercalated ions from the electrochemical LPE protocol favorably alter the optical response of the α-RuCl₃ nanosheets, enabling large-area Mott insulator photodetectors that operate at telecommunications-relevant infrared wavelengths near 1.55 μm. These photodetectors show a linear photocurrent response as a function of incident power, which suggests negligible trap-mediated recombination or photothermal effects, ultimately resulting in a photoresponsivity of ≈2 mA/W.

White-Light-Driven Resonant Emission from a Monolayer Semiconductor

Resonant emission in photonic structures is very useful to construct all-photonic circuits for optical interconnects and quantum computing. Optical generation of most resonant-emitting modes in photonic structures is obtained by coherent pumping rather than incoherent illumination. Particularly, the development of white-light- or even solar-powered on-chip light sources remains challenging but is very attractive in view of the much facile availability of these incoherent excitation sources. Here, net resonant emission from a monolayer semiconductor is demonstrated under simulated solar illumination by a white-light-emitting diode. The device is formed by embedding a 2D gain medium into a planar microcavity on a silicon wafer, which is compatible with the prevailing on-chip photonic technology. Coherent and white-light excitation sources are, respectively, selected for optical pumping, where the output light in two cases exhibits well-consistent resonant wavelength, linewidth, polarization, location, and Gaussian-beam profile. The fundamental TEM₀₀ mode behaves as a doublet emission, resulting from anisotropy-induced non-degenerate states with orthogonal polarizations. The extraordinary spectral flipping is attributed to the competitive interplay of resonant absorption and emission. This work paves a way toward white-light or solar-powered state-of-the-art photonic applications at the chip scale.

2D materials beyond graphene toward Si integrated infrared optoelectronic devices

Since the discovery of graphene in 2004, it has become a worldwide hot topic due to its fascinating properties. However, the zero band gap and weak light absorption of graphene strictly restrict its applications in optoelectronic devices. In this regard, semiconducting two-dimensional (2D) materials are thought to be promising candidates for next-generation optoelectronic devices. Infrared (IR) light has gained intensive attention due to its vast applications, including night vision, remote sensing, target acquisition, optical communication, etc. Consequently, the generation, modulation, and detection of IR light are crucial for practical applications. Due to the van der Waals interaction between 2D materials and Si, the lattice mismatch of 2D materials and Si can be neglected; consequently, the integration process can be achieved easily. Herein, we review the recent progress of semiconducting 2D materials in IR optoelectronic devices. Firstly, we introduce the background and motivation of the review. Then, the suitable materials for IR applications are presented, followed by a comprehensive review of the applications of 2D materials in light emitting devices, optical modulators, and photodetectors. Finally, the problems encountered and further developments are summarized. We believe that milestone investigations of IR optoelectronics based on 2D materials beyond graphene will emerge soon, which will bring about great industrial revelations in 2D material-based integrated nanodevice commercialization.

Wavelength-Tunable Mid-Infrared Lasing from Black Phosphorus Nanosheets

Van der Waals layered semiconductor materials own unique physical properties and have attracted intense interest in developing high-performance electronic and photonic devices. Among them, black phosphorus (BP) is distinct for its layer number-tuned direct band gap which spans from near- to mid-infrared (MIR) waveband. In addition, the puckered honey comb crystal lattice endows the material with highly linear-polarized emission and marked anisotropy in carrier transportation. These unique material properties render BP as an intriguing and promising building block for constructing mid-infrared-ranged coherent light sources. Here, a room temperature surface-emitting MIR laser based on single crystalline BP nanosheets coupled with a distributed Bragg reflector cavity is reported. MIR stimulated emission at 3611 nm is achieved with a near-unity linear polarization, which exhibits robust thermal stability up to 360 K. Most importantly, the lasing wavelength can be tuned from 3425 to 4068 nm by varying the cavity length via thickness control of BP layer. The demonstrated highly polarized lasing output and wavelength-tunable capacity of the proposed device scheme in MIR spectral range opens up promising opportunities for a broad array of applications in polarization-resolved IR imaging, range-finding, and free space quantum communications.

Concentrically Integrative Bioassembly of a Three-Dimensional Black Phosphorus Nanoscaffold for Restoring Neurogenesis, Angiogenesis, and Immune Homeostasis

Black phosphorus is well known for its excellent electromechanical properties. Although it has previously been used for therapeutic drug delivery in cancer, it has never been applied as an electroactive polymer for post-trauma tissue regeneration (e.g., in cardiac muscles and neurons). The major concern currently preventing such applications is its controversial biosafety profile in vivo. Here, we demonstrate the production of a concentrically integrative layer-by-layer bioassembled black phosphorus nanoscaffold. This scaffold has remarkable electrical conductivity, permitting smooth release into the surrounding microenvironment. We confirmed that, under mild oxidative stress, our black phosphorus nanoscaffold induced angiogenesis and neurogenesis and stimulated calcium-dependent axon regrowth and remyelination. Long-term in vivo implantation of this nanoscaffold during severe neurological defect regeneration induced negligible toxicity levels. These results provide new insight into the regenerative capability of manufactured 3D scaffolds using neuroengineered 2D black phosphorus nanomaterials.

2D-Organic Hybrid Heterostructures for Optoelectronic Applications

The unique properties of hybrid heterostructures have motivated the integration of two or more different types of nanomaterials into a single optoelectronic device structure. Despite the promising features of organic semiconductors, such as their acceptable optoelectronic properties, availability of low-cost processes for their fabrication, and flexibility, further optimization of both material properties and device performances remains to be achieved. With the emergence of atomically thin 2D materials, they have been integrated with conventional organic semiconductors to form multidimensional heterostructures that overcome the present limitations and provide further opportunities in the field of optoelectronics. Herein, a comprehensive review of emerging 2D-organic heterostructures-from their synthesis and fabrication to their state-of-the-art optoelectronic applications-is presented. Future challenges and opportunities associated with these heterostructures are highlighted.