III-V semiconductors such as GaAs are widely studied as promising candidates for high-speed integrated circuit. Despite these applications for conventional bulk structures, their fundamental physical properties in the nanoscale limit are still in scarcity, which is of great importance for the development of nanoelectronics. In this work, we demonstrate that the III-V semiconductor MX (M = Al, Ga, In; X = P, As, Sb) in its two-dimensional (2D) limit could exhibit double layer honeycomb (DLHC) configuration and distorted tetrahedral coordination, according to our first-principles calculations with HSE06 hybrid functional. It is found that surface reconstruction endows 2D III-V DLHCs with pronouncedly different electronic and magnetic properties from their bulk counterparts due to strong interlayer coupling. Mexican-hat-shape bands emerge at the top valence bands of pristine AlP, GaP, InP, AlAs, and InAs DLHCs, inducing the density of states showing a sharp van Hove singularity near the Fermi level. As a result, these DLHCs exhibit itinerant magnetism upon moderate hole doping, while the rest GaAs, AlSb, GaSb, and InSb DLHCs become magnetic under tensile strain with hole doping. With an exchange splitting of the localized p_z states at the top valence bands, the hole-doped III-V DLHCs become half-metals with 100% spin-polarization. Remarkably, the InSb DLHC shows inverted band structure near the Fermi level, bringing about nontrivial topological band structures in stacked InSb DLHC due to the strong spin-orbital coupling. These III-V DLHCs expand the members of 2D material family and their exotic magnetic and topological properties may offer great potential for applications in the novel electronic and spintronic devices.

Growth of high-quality large-sized crystals using the traditional chemical vapor transport (CVT) or vertical Bridgman (VB) technique is costly and time-consuming, limiting its practical industrial application. Here, we propose an ultrafast crystal growth process with low energy consumption and capability of producing crystals of excellent quality, and demonstrate that large-sized GaSe crystals with a lateral size of 0.5 to 1 cm can be obtained within a short period of 5 min. X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) studies clearly indicate that the as-grown crystals have a good crystallinity. To further show the potential application of the resulting GaSe crystals, we fabricate the few-layer GaSe-based photodetector, which exhibits low dark current of 21 pA and fast response of 34 ms under 405 nm illumination. Our proposed technique for rapid crystal growth could be further extended to other metallenes with low-melting point, such as Bi-, Sn-, In-, Pb-based crystals, opening up a new avenue in fulfilling diverse potential optoelectronics applications of two-dimensional (2D) crystals.

Leveraging the unique physical properties, two-dimensional (2D) materials have circumvented the disadvantages of conventional epitaxial semiconductors and held great promise for potential optoelectronic applications. So far, two main detector architectures including photodiode based on a van der Waals P-N junction or Schottky junction and phototransistor based on individual 2D materials or hybrids have been well developed. However, a trade-off between responsivity and speed always exists in those technologies thus hindering the overall performance improvement. Here, we propose a new device concept by sandwiching the 2D anisotropic semimetal between p-type and n-type semiconductors in the out-of-plane direction, called PSN architecture, realizing the improvement of each parameter including broad spectral coverage, fast speed, high sensitivity, power-free and polarization-sensitive. We stack the p-type 2H-MoTe₂, Weyl semimetal 1T-MoTe₂ and n-type SnSe₂ layer-by-layer constructing vertical sandwich structure where the top and bottom layers contribute to the internal built-in electric field, the intermediate layer can facilitate the exciton dissociation and act as infrared polarized light sensitizers. As a result, this PSN device exhibits broadband photo-response from 405 to 1,550 nm without external bias supply. At optical communication band (1,310 nm), operating at self-driven mode and room temperature, the responsivity and detectivity can reach up to 64.2 mA·W^–1 and 2.2×10¹¹ Jones, respectively, along with fast speed on the order of millisecond. Moreover, the device simultaneously exhibits exceptional detection capability for infrared polarized light, demonstrating the anisotropic photocurrent ratio of 1.55 at 1,310 nm and 2.02 at 1,550 nm, which is attributed to the strong in-plane optical anisotropy of middle 1T-MoTe₂ layer. This work develops a new photodetector scheme with novel PSN architecture toward broadband, self-power, polarized light sensing and imaging modules.