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GeSe is a layered p-type semiconductor with intriguing optoelectrical properties such as high absorption coefficient, high carrier mobility, and narrow bandgap, which promises a broadband photoresponse over a wide spectral range. However, GeSe based broadband photodetectors could not achieve both high responsivity and fast response speed. Therefore, it is urgent to improve the properties of GeSe based broadband photodetectors. Herein, a GeSe/MoTe2 van der Waals (vdW) heterostructure was designed. The GeSe/MoTe2 vdW heterostructure possesses broadband photodetection over ultraviolet, visible, and near infrared. The device has competitive responsivity (R) and detectivity (D*) over a broadband even at 1050 nm, which are 28.4 A/W and 5.6 × 109 Jones, respectively. Excitingly, the response speed for 365 nm is as fast as 3 μs, which is much faster than most other GeSe devices. Overall, our results suggest that the GeSe/MoTe2 heterostructure can provide an effective strategy to achieve broadband photodetectors with both high responsivity and fast response. [ABSTRACT FROM AUTHOR]

Light manipulation has promoted applications in all‐optical processing. 2D anisotropic rare earth (RE) materials are promising for light modulation to realize information transmission and encryption due to the unique optical behaviors of RE ions. Here, image transmission and encryption have been realized by using 2D anisotropic RE material Eu2O3. The polarized photoluminescence (PL) of Eu2O3 has been innovatively applied for information transmission by switching the on/off states. The opposite two modes of polarization‐dependent PL have been applied to grayscale‐resolved image transmission and encryption with high security. This novel approach, polarization manipulation on the PL of 2D anisotropic RE materials, will shed light on the development of information processing, all‐optical switch, and all‐optical computation. [ABSTRACT FROM AUTHOR]

2D materials have shown great promise for next‐generation high‐performance photodetectors. However, the performance of photodetectors based on 2D materials is generally limited by the tradeoff between photoresponsivity and photodetectivity. Here, a novel junction field‐effect transistor (JFET) photodetector consisting of a PdSe2 gate and MoS2 channel is constructed to realize high responsivity and high detectivity through effective modulation of top junction gate and back gate. The JFET exhibits high carrier mobility of 213 cm2 V−1 s−1. What is more, the high responsivity of 6 × 102 A W−1, as well as the high detectivity of 1011 Jones, are achieved simultaneously through the dual‐gate modulation. The high performance is attributed to the modulation of the depletion region by the dual‐gate, which can effectively suppress the dark current and enhance the photocurrent, thereby realizing high detectivity and responsivity. The JFET photodetector provides a new approach to realize photodetectors with high responsivity and detectivity. [ABSTRACT FROM AUTHOR]

2D rare earth (RE) materials have received considerable attention in recent years due to the fascinating luminescence, magnetism, and electric properties originated from RE associated with sharp and various emission peaks, intrinsic 2D ferromagnetism, and incommensurate charge density wave. These materials might open up a new prospect in next‐generation lighting, magnetic devices, and phototransistors. Herein, a comprehensive review of 2D RE materials is presented, focusing on their recent progresses. First, the crystal structures of 2D RE materials are discussed. Then, typical synthesis methods such as mechanical exfoliation, molecular beam epitaxy, pulsed laser deposition, and chemical vapor deposition are introduced. Furthermore, various properties in luminescence, magnetism, and electronics are summarized. The recently reported RE‐based 2D novel photodetectors are outlined as three constructions: MoS2/RE, graphene/RE, and perovskite/RE, which show promising applications for both narrow and broad band detection arised from the special absorption windows of different RE elements. Finally, the conclusions and outlook of this area are proposed, such as exploring novel 2D RE compounds, improving stability, and broadening applications. [ABSTRACT FROM AUTHOR]

Polarized photodetection based on anisotropic two‐dimensional materials display promising prospects for practical application in optical communication and optoelectronic fields. However, most of the reported polarized photodetection are limited by the lack of valid tunable strategy and low linear dichroism ratio. A peculiar noble metal dichalcogenide—PdSe2 with a puckered pentagonal structure and abnormal linear dichroism conversion—potentially removes these restrictions and is demonstrated in this study. Herein, azimuth‐dependent reflectance difference microscopy combined with anisotropic electrical transport measurements indicate strong in‐plane anisotropic optical and electrical properties of two‐dimensional PdSe2. Remarkably, the typical polarization‐resolved photodetection exhibits anisotropic photodetection characteristics with a dichroic ratio up to ≈1.8 at 532 nm and ≈2.2 at 369 nm, and their dominant polarization orientation differs by 90° corresponding to the a‐axis and b‐axis, respectively. The unique orientation selection behavior in polarization‐dependent photodetection can be attributed to the intrinsic linear dichroism conversion. The results make 2D PdSe2 a promising platform for investigating anisotropic structure–property correlations and integrated optical applications for novel polarization‐sensitive photodetection. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) is a rapidly up and coming star in two‐dimensional (2D) materials. The unique characteristic of BP is its in‐plane anisotropy. This characteristic of BP ignites a new type of 2D materials that have low‐symmetry structures and in‐plane anisotropic properties. On this basis, they offer richer and more unique low‐dimensional physics compared to isotropic 2D materials, thus providing a fertile ground for novel applications including electronics, optoelectronics, molecular detection, thermoelectric, piezoelectric, and ferroelectric with respect to in‐plane anisotropy. This article reviews the recent advance in characterization and applications of in‐plane anisotropic 2D materials. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) ferroelectrics have attracted intensive attention. However, the 2D ferroelectrics remain rare, and especially few of them represent high ferroelectric transition temperature ( T C ), which is important for the usability of ferroelectrics. Herein, CuCrS 2 nanoflakes are synthesized by salt-assisted chemical vapor deposition and exhibit switchable ferroelectric polarization even when the thickness is downscaled to 6 nm. On the contrary, a CuCrS 2 nanoflake shows a T C as high as ∼700 K, which can be attributed to the robust tetrahedral bonding configurations of Cu cations. Such robustness can be further clarified by a theoretically predicted high order-disorder transition barrier and structure evolution from 600 to 800 K. Additionally, the interlocked out-of-plane (OOP) and in-plane (IP) ferroelectric domains are observed and two kinds of devices based on OOP and IP polarizations are demonstrated.

Two-dimensional (2D) ferroelectric materials have attracted increasing interest due to meeting the requirements of integration, miniaturization, and multifunction of devices. However, the exploration of intrinsic 2D ferroelectric materials is still in the early stage, for which the related reports are still limited, especially fewer ones prepared by chemical vapor deposition (CVD). Here, the ultrathin metal-tellurium-oxyhalide Cd 7 Te 7 Cl 8 O 17 (CTCO) flakes as thin as 3.8 nm are realized via the selenium-induced selective-bonding CVD method. The growth mechanism has been confirmed by experiments and theoretical calculations, which can be ascribed to the induction of selective bonding of a hydrogen atom in H 2 O molecules by the introduction of selenium, leading to the generation of strong oxidants. Excitingly, switchable out-of-plane ferroelectric polarization was observed in CTCO flakes down to 6 nm at room temperature, which may be caused by mobile Cl vacancies. This work has implications for the synthesis and applications of 2D ferroelectric materials.

van der Waals (vdW) heterostructures based on atomically thin 2D materials have led to a new era in next-generation optoelectronics due to their tailored energy band alignments and ultrathin morphological features, especially in photodetectors. However, these photodetectors often show an inevitable compromise between photodetectivity and photoresponsivity with one high and the other low. Herein, a highly sensitive WSe 2 /SnS 2 photodiode is constructed on BN thin film by exfoliating each material and manually stacking them. The WSe 2 /SnS 2 vdW heterostructure shows ultralow dark currents resulting from the depletion region at the junction and high direct tunneling current when illuminated, which is confirmed by the energy band structures and electrical characteristics fitted with direct tunneling. Thus, the distinctive WSe 2 /SnS 2 vdW heterostructure exhibits both ultrahigh photodetectivity of 1.29 × 10 13 Jones (I ph /I dark ratio of ≈10 6 ) and photoresponsivity of 244 A W -1 at a reverse bias under the illumination of 550 nm light (3.77 mW cm -2 )., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)