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.

Emerging classes of 2D noble-transition-metal dichalcogenides (NTMDs) stand out for their unique structure and novel physical properties in recent years. With the nearly full occupation of the d orbitals, 2D NTMDs are expected to be more attractive due to the unique interlayer vibrational behaviors and largely tunable electronic structures compared to most transition metal dichalcogenide semiconductors. The novel properties of 2D NTMDs have stimulated various applications in electronics, optoelectronics, catalysis, and sensors. Here, the latest development of 2D NTMDs are reviewed from the perspective of structure characterization, preparation, and application. Based on the recent research, the conclusions and outlook for these rising 2D NTMDs are presented.Very recently, group-10 noble TMDs (NTMDs) have been reintroduced as new 2D materials, displaying many fascinating properties including widely tunable bandgap, moderate carrier mobility, anisotropy, and ultrahigh air stability. [34][35][36][37] Unlike most common TMDs with less d-electrons, the d orbitals of NTMDs are nearly fully occupied, and the corresponding p z orbital of interlayer chalcogen atoms are highly hybridized, leading to strong layer-dependent properties and interlayer interactions. [36,38] For example, it has been predicted that PtS 2 holds a layerdependent bandgap from 0.25 to 1.6 eV, [36] bridging the gap between graphene and most TMDs that with large gap. Besides, the calculated mobility based on PtS 2 , PtSe 2 , and PdSe 2 field effect transistors (FETs) is as high as ≈200 cm 2 V −1 s −1 , [36,37,39] larger than most other TMDs. Moreover, NTMDs possess high air stability, and the performance of the PtSe 2 FET remains nearly unchanged after 5 months air exposure. [37] Specially, PdS 2 and PdSe 2 hold novel puckered pentagonal structure and thus exhibit very interesting anisotropic properties, [39,40] which may bring even more physics and applications. Additionally, PtTe 2 and PdTe 2 are type-II Dirac fermions, making them great platform for investigating novel transport related to topological phase transition and chiral anomaly. [41,42] Nowadays, the 2D NTMDs is becoming increasingly fascinating in the 2D materials research.In this review, we highlight a comprehensive report of the recent research progress in 2D NTMDs such as PtS 2 , PtSe 2 , PdS 2 , PdSe 2 , PtTe 2 , and PdTe 2 . In order to understand the internal relation between structural characteristics and physical properties, this review begins with a brief summary of the structure of 2D NTMDs and their transitions. Then, some recent progress on their preparation methods, including mechanical exfoliation of the bulk materials, chemical vapor deposition (CVD), molecular beam epitaxy (MBE), is reviewed along with the performance of the resulting 2D NTMDs as high-performance candidate for field effect transistors, photodetectors, catalysis, and sensors. Finally, this review is concluded with the existing challenges and a future perspective for these rising 2D NTMDs. Structure of 2D NTM...

As an emerging two-dimensional semiconductor, Bi 2 O 2 Se has recently attracted broad interests in optoelectronic devices for its superior mobility and ambient stability, whereas the diminished photoresponse near its inherent indirect bandgap (0.8 eV or λ = 1550 nm) severely restricted its application in the broad infrared spectra. Here, we report the Bi 2 O 2 Se nanosheets based hybrid photodetector for short wavelength infrared detection up to 2 μm via PbSe colloidal quantum dots (CQDs) sensitization. The type II interfacial band offset between PbSe and Bi 2 O 2 Se not only enhanced the device responsivity compared to bare Bi 2 O 2 Se but also sped up the response time to ∼4 ms, which was ∼300 times faster than PbSe CQDs. It was further demonstrated that the photocurrent in such a zero-dimensional−two-dimensional hybrid photodetector could be efficiently tailored from a photoconductive to photogate dominated response under external field effects, thereby rendering a sensitive infrared response >10 3 A/W at 2 μm. The excellent performance up to 2 μm highlights the potential of field-effect modulated Bi 2 O 2 Se-based hybrid photodetectors in pursuing highly sensitive and broadband photodetection.

Two-dimensional molecular crystals, consisting of zero-dimensional molecules, are very appealing due to their novel physical properties. However, they are mostly limited to organic molecules. The synthesis of inorganic version of two-dimensional molecular crystals is still a challenge due to the difficulties in controlling the crystal phase and growth plane. Here, we design a passivator-assisted vapor deposition method for the growth of two-dimensional Sb2O3 inorganic molecular crystals as thin as monolayer. The passivator can prevent the heterophase nucleation and suppress the growth of low-energy planes, and enable the molecule-by-molecule lateral growth along high-energy planes. Using Raman spectroscopy and in situ transmission electron microscopy, we show that the insulating α-phase of Sb2O3 flakes can be transformed into semiconducting β-phase under heat and electron-beam irradiation. Our findings can be extended to the controlled growth of other two-dimensional inorganic molecular crystals and open up opportunities for potential molecular electronic devices.

Due to the intriguing anisotropic optical and electrical properties, low‐symmetry 2D materials are attracting a lot of interest both for fundamental studies and fabricating novel electronic and optoelectronic devices. Identifying new promising low‐symmetry 2D materials will be rewarding toward the evolution of nanoelectronics and nano‐optoelectronics. In this work, germanium diarsenide (GeAs2), a group IV–V semiconductor with novel low‐symmetry puckered structure, is introduced as a favorable highly anisotropic 2D material into the rapidly growing 2D family. The structural, vibrational, electrical, and optical in‐plane anisotropy of GeAs2 is systematically investigated both theoretically and experimentally, combined with thickness‐dependent studies. Polarization‐sensitive photodetectors based on few‐layer GeAs2 exhibit highly anisotropic photodetection behavior with lineally dichroic ratio up to ≈2. This work on GeAs2 will excite interests in the less exploited regime of group IV–V compounds.

Benefiting from the superior electron mobility and good air‐stability, the emerging layered bismuth oxyselenide (Bi2O2Se) nanosheet has received considerable attention with the promising prospects for electronics and optoelectronics applications. However, the high charge carrier concentration and bolometric effect of Bi2O2Se give rise to the high dark current and relatively slow photoresponse, which severely impede further improvement of the performance of Bi2O2Se based photodetectors. Here, a WSe2/Bi2O2Se Van der Waals p‐n heterostructure is reported with a pronounced rectification ratio of 105 and a low reverse dark current of 10−11 A, as well as an enhanced light on/off ratio up to 618 under 532 nm light illumination. The device also exhibits a fast response speed of 2.6 µs and a broadband detection capability from 365 to 2000 nm due to the efficient charge separation and strong interlayer coupling at the interface of the two flakes. Importantly, the built‐in potential in the WSe2/Bi2O2Se heterostructure offers a competitive self‐powered photodetector with the light on/off ratio above 105 and a photovoltaic responsivity of 284 mA W−1. The WSe2/Bi2O2Se heterostructure shows promising potentials for high‐performance self‐driven photodetector applications.

Broken-gap van der Waals (vdW) heterojunctions based on 2D materials are promising structures to fabricate high-speed switching and low-power multifunctional devices thanks to its charge transport versus quantum tunneling mechanism. However, the tunneling current is usually generated under both positive and negative bias voltage, resulting in small rectification and photocurrent on/off ratio. In this paper, we report a broken-gap vdW heterojunction PtS2/WSe2 with a bilateral accumulation region design and a big band offset by utilizing thick PtS2 as an effective carrier-selective contact, which exhibits an ultrahigh reverser rectification ratio approaching 108 and on/off ratio over 108 at room temperature. We also find excellent photodetection properties in such a heterodiode with a large photocurrent on/off ratio over 105 due to its ultralow forward current and a comparable photodetectivity of 3.8 × 1010 Jones. In addition, the response time of such a photodetector reaches 8 μs owing to the photoinduced tunneling mechanism and reduced interface trapping effect. The proposed heterojunction not only demonstrates the high-performance broken-gap heterodiode but also provides in-depth understanding of the tunneling mechanism in the development of future electronic and optoelectronic 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.