Abstract2D GeSe possesses black phosphorous‐analog‐layered structure and shows excellent environmental stability, as well as highly anisotropic in‐plane properties. Additionally, its high absorption efficiency in the visible range and high charge carrier mobility render it promising for applications in optoelectronics. However, most reported GeSe‐based photodetectors show frustrating performance especially in photoresponsivity. Herein, a 2D GeSe‐based phototransistor with an ultrahigh photoresponsivity is demonstrated. Its optimized photoresponsivity can be up to ≈1.6 × 105 A W−1. This high responsivity can be attributed to the highly efficient light absorption and the enhanced photoconductive gain due to the existence of trap states. The exfoliated GeSe nanosheet is confirmed to be along the [001] (armchair direction) and [010] (zigzag direction) using transmission electron microscopy and anisotropic Raman characterizations. The angle‐dependent electric and photoresponsive performance is systematically explored. Notably, the GeSe‐based phototransistor shows strong polarization‐dependent photoresponse with a peak/valley ratio of 1.3. Furthermore, the charge carrier mobility along the armchair direction is measured to be 1.85 times larger than that along the zigzag direction.

Infrared detection at optical communication wavelength is of great significance because of their diverse commercial and military communication applications. The layered Bi2Se3 with a narrow band gap of 0.3 eV is regarded as a promising candidate toward high‐performance terahertz to infrared applications. However, the controllable synthesis of large‐size ultrathin Bi2Se3 flakes remains a challenge owing to complex nucleation process and infrared telecommunication photodetectors based on Bi2Se3 flakes are rarely reported. Here, large size (submillimeter: 0.2–0.4 mm in lateral dimensions) and ultrathin (thickness: 3 nm to few nanometers) 2D Bi2Se3 flakes with high crystal quality are obtained by suppressing the nucleation density. More importantly, back‐gate field‐effect transistor based on Bi2Se3 flake exhibits an ultrahigh on/off current ratio of 106 and competitive mobility of 39.4 cm2 V−1 s−1. Moreover, excellent on/off ratio of 972.5, responsivity of 23.8 A W−1, and external quantum efficiency of 2035% are obtained from Bi2Se3‐based photodetector at 1456 nm in the E‐band of the telecommunication range. With controlled morphology and excellent photoresponse performance, the Bi2Se3 photodetector shows great potential in the optoelectronic field including communications, military, and remote sensing.

Due to the predicted excellent electronic properties superior to group VIB (Mo and W) transition metal dichalcogenides (TMDs), group IVB TMDs have enormous potential in nanoelectronics. Here, the synthesis of ultrathin HfS 2 flakes via space-confined chemical vapor deposition, realized by an inner quartz tube, is demonstrated. Moreover, the effect of key growth parameters including the dimensions of confined space and deposition temperature on the growth behavior of products is systematically studied. Typical as-synthesized HfS 2 is a hexagonal-like flake with a smallest thickness of ≈1.2 nm (bilayer) and an edge size of ≈5 µm. The photodetector based on as-synthesized HfS 2 flakes demonstrates excellent optoelectronic performance with a fast photoresponse time (55 ms), which is attributed to the high-quality crystal structure obtained at a high deposition temperature and the ultraclean interface between HfS 2 and the mica substrate. With such properties HfS 2 holds great potential for optoelectronics applications.

Van der Waals (vdW) dielectrics such as hBN are widely used to preserve the intrinsic properties of twodimensional (2D) semiconductors and support the fabrication of high-performance 2D devices. This is fundamentally attributed to their dangling-bond-free surface, carrying far lower density of charged scattering sources and trap states with respect to the conventional dielectrics (SiO 2 etc.). However, their wafer-scale fabrication and compatible integration with 2D semiconductors remain cumbersome, giving rise to the di culties in scalable fabrication of high-performance 2D devices. Here we report a high-κ vdW dielectric (ε r =11.5) composed of inorganic molecular crystal (IMC) Sb 2 O 3 , allowing for large-scale fabrication and facile integration via standard thermal evaporation process thanks to its particular crystal structure. Similarly, our vdW dielectric also supports remarkably improved 2D devices with respect to the typical conventional dielectric SiO 2 . The monolayer MoS 2 eld effect transistors (FET) supported by our vdW dielectric exhibits high on/off ratio (10 8 ), greatly enhanced electron mobility (from 20 to 80 cm 2 /Vs) and reduced transfer-curve hysteresis over an order of magnitude. Our results may open a new avenue towards compatible fabrication of vdW dielectrics using IMCs and lead to the scalable fabrication of high-performance 2D devices.

Since the first isolation of graphene in 2004, [1] 2D materials have gained growing attention because of their unique physical and physicochemical properties, [2,3] originating from their reduced dimensions, [4] strong electron confinement, [5] abundant active sites, [6] and edge polarization. [7] These features, in turn, endow 2D materials with exciting prospects for promising applications in the fields of energy storage/conversion and optoelectronics. In the early stages, the research on 2D materials was primarily focused on single or binary elemental materials. [8][9][10][11][12][13] Recently, however, 2D ternary materials have attracted increasing attention due to their multiple degrees of freedom. [14][15][16][17][18][19][20] The added freedom of stoichiometry variation in 2D ternary materials can be used to tune their physical properties and therefore may lead to promising applications. [21,22] Ternary Ga 2 In 4 S 9 is a layered material with weak van der Waals interaction and reveals n-type semiconducting behavior. [23,24] The multinary compound that reveals an unprecendented robust electronic character as well as a wide bandgap close to 2.7 eV with pronounced photosensitivity and temperature-dependent optical absorption edge opens a new paradigm for UV detection. [23] This is particularly desirable for military and civilian fields. [25] Specifically, as a kind of homobimetallic sulfide, the ternary Ga 2 In 4 S 9 is believed to possess novel electronic and optoelectronic properties compared the 2D counterparts. [26] Up to now, only work on bulk Ga 2 In 4 S 9 with a thickness of a few micrometers has been reported, in which bulk Ga 2 In 4 S 9 is obtained by chemical vapor transport. [23,27] The bulk structure actually hinders their practical application in the field of micro-nano electronic and optoelectronic devices. [28] Unfortunately, there are no reports on the synthesis of 2D ternary Ga 2 In 4 S 9 flakes with controllable stoichiometry, which may be attributed to the difficulty in selecting optimal homobimetallic precursors. Recently, the creation of atomically thin metal oxides or selenides by adopting eutectic gallium melts with tunable metal elements offers a promising approach to grow ternary semiconductors. [29][30][31][32] In this letter, we report the growth of ultrathin Ga 2 In 4 S 9 flakes by employing liquid gallium/indium (Ga/In) alloy as the reaction environment. Because of the reduced reaction temperature by using the liquid Ga/In alloy, [31] the key point of our growth 2D ternary systems provide another degree of freedom of tuning physical properties through stoichiometry variation. However, the controllable growth of 2D ternary materials remains a huge challenge that hinders their practical applications. Here, for the first time, by using a gallium/indium liquid alloy as the precursor, the synthesis of high-quality 2D ternary Ga 2 In 4 S 9 flakes of only a few atomic layers thick (≈2.4 nm for the thinnest samples) through chemical vapor deposition is realized. Their UV-light-sensing appl...

2D nonlayered materials that possess appealing properties are entering the researchers' vision. However, direct access to the 2D level of these materials is still a great challenge due to the instrinsic isotropic chemical bond. This work presents the initially self-limited epitaxial growth of ultrathin nonlayered CdS flakes (as thin as 6 nm) on mica substrate with a large domain size (>40 µm) by employing In 2 S 3 as the passivation agent. Besides, the thickness and sizes of the products could be tunable by the addition level of In 2 S 3 amount. The growth mechanism is evidenced via experiments and theoretical calculations, which is attributed to the surface distortion effect of In-S motif and the preference of local environments for In on the CdS (0001) surface. The photodetector designed on CdS flake demonstrates a high photoswitching ratio (up to 10 3 ), a high detectivity (D* ≈ 2.71 × 10 9 Jones), and fast photoresponse speed (τ R = 14 ms, τ D = 8 ms). The as-proposed self-limited epitaxial growth method opens a new avenue to synthetize 2D nonlayered materials and will promote their further applications in novel optoelectronic devices.photoresponse speed (τ R = 14 ms, τ D = 8 ms), indicating high promising applications in optoelectronics. The present self-limited epitaxial growth method opens a new avenue to synthetize 2D nonlayered materials.

2D nonlayered materials have attracted intensive attention due to their unique surface structure and novel physical properties. However, it is still a great challenge to realize the 2D planar structures of nonlayered materials owing to the naturally intrinsic covalent bonds. Ge is one of them with cubic structure impeding its 2D anisotropic growth. Here, the ultrathin single-crystalline Ge flakes as thin as 8.5 nm were realized via halide-assisted self-limited CVD growth. The growth mechanism has been confirmed by experiments and theoretical calculations, which can be attributed to the preferential growth of the (111) plane with the lowest formation energy and the giant interface distortion effect of the Cl-Ge motif. Excitingly, a Ge flake-based phototransistor shows excellent performances such as a high hole mobility of ∼263 cm V s, a high responsivity of ∼200 A/W, and fast response rates (τ = 70 ms, τ = 6 ms), suggesting its great potential in the applications of electronics and optoelectronics.

No abstract