Mid-infrared (IR) detectors based on the emerging low-dimensional (two-dimensional and quasi one-dimensional) materials offer unique characteristics including large bandgap tunability, optical polarization sensitivity and integrability with typical silicon process, which are not available in the mid-IR detectors based on traditional compound semiconductors. Here, we review the recent progress in study of mid-IR detectors based on the low-dimensional materials, including black phosphorus, black arsenic phosphorus, tellurene and BaTiS₃, from the perspectives of crystal structure, material synthesis, optical properties, and the detector characteristics. The detector gain and detectivity are benchmarked, and the unique properties, such as the polarization sensitivity, are discussed. We also provide our perspective about key future research directions in this field.

In the past few years, two-dimensional (2D) transition metal dichalcogenide (TMDC) materials have attracted increasing attention of the research community, owing to their unique electronic and optical properties, ranging from the valley–spin coupling to the indirect-to-direct bandgap transition when scaling the materials from multi-layer to monolayer. These properties are appealing for the development of novel electronic and optoelectronic devices with important applications in the broad fields of communication, computation, and healthcare. One of the key features of the TMDC family is the indirect-to-direct bandgap transition that occurs when the material thickness decreases from multilayer to monolayer, which is favorable for many photonic applications. TMDCs have also demonstrated unprecedented flexibility and versatility for constructing a wide range of heterostructures with atomic-level control over their layer thickness that is also free of lattice mismatch issues. As a result, layered TMDCs in combination with other 2D materials have the potential for realizing novel high-performance optoelectronic devices over a broad operating spectral range. In this article, we review the recent progress in the synthesis of 2D TMDCs and optoelectronic devices research. We also discuss the challenges facing the scalable applications of the family of 2D materials and provide our perspective on the opportunities offered by these materials for future generations of nanophotonics technology.

In this work, we study the interlayer phonon vibration modes, the layer-numberdependent optical bandgap, and the anisotropic photoluminescence (PL) spectra of atomically thin rhenium diselenide (ReSe₂) for the first time. The ultralow frequency interlayer Raman spectra and the polarization-resolved high frequency Raman spectra in ReSe₂ allow the identification of its layer number and crystal orientation. Furthermore, PL measurements show the anisotropic optical emission intensity of the material with its bandgap increasing from 1.26 eV in the bulk to 1.32 eV in the monolayer. The study of the layer-number dependence of the Raman modes and the PL spectra reveals relatively weak van der Waal's interaction and two-dimensional (2D) quantum confinement in the atomically thin ReSe₂. The experimental observation of the intriguing anisotropic interlayer interaction and tunable optical transition in monolayer and multilayer ReSe₂ establishes the foundation for further exploration of this material in the development of anisotropic optoelectronic devices functioning in the near-infrared spectrum, which is important for many applications in optical communication and infrared sensing.