Transition metal dichalcogenides (TMDCs) are promising candidates for future optoelectronic devices accounting for their high carrier mobility and excellent quantum efficiency. However, the limited light absorption efficiency in atomically thin layers significantly hinders photocarrier generation, thereby impairing the optoelectronic performance and hindering practical applications. Herein, we successfully synthesized In₂Se₃/WSe₂ heterostructures through a typical two-step chemical vapor deposition (CVD) method. The In₂Se₃ nanosheet with strong light absorption capability, serving as the light absorption layer, was integrated with the monolayer WSe₂, enhancing the photosensitivity of WSe₂ significantly. Upon laser irradiation with a wavelength of 520 nm, the In₂Se₃/WSe₂ heterostructure device shows an ultrahigh photoresponsivity with a value as high as 2333.5 A/W and a remarkable detectivity reaching up to 6.7 × 10¹² Jones, which is the highest among almost the reported TMDCs-based heterostructures grown via CVD even some fabricated by mechanical exfoliation (ME). Combing the advantages of CVD method such as large scale, high yield, and clean interface, the In₂Se₃/WSe₂ heterostructures would provide a novel path for future high-performance optoelectronic device.

With the unprecedented increasing demand for extremely fast processing speed and huge data capacity, traditional silicon-based information technology is becoming saturated due to the encountered bottlenecks of Moore's Law. New material systems and new device architectures are considered promising strategies for this challenge. Two-dimensional (2D) materials are layered materials and garnered persistent attention in recent years owing to their advantages in ultrathin body, strong light-matter interaction, flexible integration, and ultrabroad operation wavelength range. To this end, the integration of 2D materials into silicon-based platforms opens a new path for silicon photonic integration. In this work, a comprehensive review is given of the recent signs of progress related to 2D material integrated optoelectronic devices and their potential applications in silicon photonics. Firstly, the basic optical properties of 2D materials and heterostructures are summarized in the first part. Then, the state-of-the-art three typical 2D optoelectronic devices for silicon photonic applications are reviewed in detail. Finally, the perspective and challenges for the aim of 3D monolithic heterogeneous integration of these 2D optoelectronic devices are discussed.

Small contact resistance and low Schottky barrier height (SBH) are the keys to energy-efficient electronics and optoelectronics. Two-dimensional (2D) semiconductors-based field effect transistors (FETs), holding great promise for next-generation information circuits, still suffer from poor contact quality at the metal–semiconductor junction interface, which severely hinders their further applications. Here, a novel contact strategy is proposed, where Bi₂Te₃ nanosheets with high conductivity were in-situ epitaxially grown on MoS₂ as van der Waals contacts, which can effectively avoid the damage to MoS₂ caused during the device manufacturing process, leading to a high-performance MoS₂ FET. Moreover, the small work function difference between Bi₂Te₃ and MoS₂ (Bi₂Te₃: 4.31 eV, MoS₂: 4.37 eV, measured by Kelvin probe force microscopy (KPFM)), enables small band bending and Ohmic contact at the junction interface. Electrical characterizations indicate that the MoS₂ FET device with Bi₂Te₃ contacts possesses a high current on/off ratio (5 × 10⁷), large effective carrier mobility (90 cm²/(V·s)), and low flat-band SBH (60 meV), which is favorable as compared with MoS₂ FET with traditional Cr/Au electrodes contacts, and superior to the vast majority of the reported chemical vapor deposition (CVD) MoS₂-based FET device. The demonstration of epitaxial van der Waals Bi₂Te₃ contacts will facilitate the application of 2D MoS₂ nanosheet in next-generation low-power consumption electronics and optoelectronics.

Optoelectronic synaptic elements are emerging functional devices for the vigorous development of advanced neuromorphic computing technology in the post-Moore era. However, optoelectronic devices based on transition metal dichalcogenides (TMDs) are limited to their poor mobilities and weak light-matter interactions, which still hardly exhibit superior device performances in the application of artificial synapses. Here, we demonstrate the successful fabrication of Au nanoparticle-coupled MoS₂ heterostructures via chemical vapor deposition (CVD), where the light absorption of MoS₂ is greatly enhanced and engineered by plasmonic effects. Hot electrons are excited from Au nanoparticles, and then injected into MoS₂ semiconductors under the light illumination. The plasmonically-engineered photo-gating effect at the metal-semiconductor junction is demonstrated to create optoelectronic devices with excellent synaptic behaviors, especially in ultra-sensitive excitatory postsynaptic current (EPSC, 9.6 × 10^–3 nA@3.4 nW·cm^–2), ultralow energy consumption (34.7 pJ), long-state retention time (> 1,000 s), and tunable synaptic plasticity transitions. The material system of Au-nanoparticles coupled TMDs presents unique advantages for building artificial synapses, which may lead the future development of neuromorphic electronics in optical information sensing and learning.

Monolayer MoS₂ is a direct band gap semiconductor with large exciton binding energy, which is a promising candidate for the application of ultrathin optoelectronic devices. However, the optoelectronic performance of monolayer MoS₂ is seriously limited to its growth quality and carrier mobility. In this work, we report the direct vapor growth and the optoelectronic device of vertically-stacked MoS₂/MoSe₂ heterostructure, and further discuss the mechanism of improved device performance. The optical and high-resolution atomic characterizations demonstrate that the heterostructure interface is of high-quality without atomic alloying. Electrical transport measurements indicate that the heterostructure transistor exhibits a high mobility of 28.5 cm²/(V·s) and a high on/off ratio of 10⁷. The optoelectronic characterizations prove that the heterostructure device presents an enhanced photoresponsivity of 36 A/W and a remarkable detectivity of 4.8 × 10¹¹ Jones, which benefited from the interface induced built-in electric field and carrier dependent Coulomb screening effect. This work demonstrates that the construction of two-dimensional (2D) semiconductor heterostructures plays a significant role in modifying the optoelectronic device properties of 2D materials.

Two-dimensional (2D) vertically stacked heterostructures based on layered transition-metal dichalcogenides (TMDCs) have remarkable potential in future applications due to their rich interlayer related properties, such as interlayer excitons, tunable interlayer band alignments. However, the controlled growth of TMDC bilayer heterostructures with preferred stacking structure remains challenging. Here, we report a two-step van der Waals epitaxial vapor growth of WSe₂/WS₂ vertically stacked bilayer heterostructures with controllable commensurate crystallographic alignments (so called AA and AB stacking), by controlling the deposition temperature. Moiré patterns were obtained in both AA and AB stacked WSe₂/WS₂ heterostructures. The stacking configuration of the vertical heterostructures was verified by the second harmonic generation signals. Photoluminescence and Raman spectroscopy studies further confirm that the heterostructures with different stacking configuration have obviously different optical properties, which is ascribed to the distinct interlayer coupling and resonance excitation between the distinguishing AA and AB stacked heterostructures. The controlled growth of AA and AB stacked heterostructures could provide an importance platform not only for fundamental researches but also for functional electronic and optoelectronic device applications.

Lead halide perovskites have received tremendous attentions recently for their excellent properties such as high light absorption coefficient and long charge carrier diffusion length. However, the stability issues and the existence of toxic lead cations have largely limited their applications in optoelectronic area. Herein, we report the synthesis and investigation of highly stable and lead-free Cs₃Bi₂I₉ perovskite nanoplates for visible light photodetection applications. The Cs₃Bi₂I₉ nanoplates were synthesized through a facile solution-processed method, which is also applicable to various substrates. The achieved nanoplates present very good crystal quality and exhibit excellent long-term stability even exposed in moist air for several months. Photodetectors were constructed based on these high-quality perovskite nanoplates for the first time, and display a maximum photoresponsivity of 33.1 mA/W under the illumination of 450 nm laser, which is six times higher than the solution-synthesized CH₃NH₃PbI₃ nanowire photodetectors. The specific detectivity of these devices can reach up to 10¹⁰ Jones. Additionally, the devices exhibit fast rise and decay time of 10.2 and 37.2 ms, respectively, and highly stable photoswitching behavior with their photoresponse well retaining under alternating light and darkness. This work opens up a new opportunity for stable and low-toxic perovskite-based optoelectronic applications.

High-performance multiphoton-pumped lasers based on cesium lead halide perovskite nanostructures are promising for nonlinear optics and practical frequency upconversion devices in integrated photonics. However, the performance of such lasers is highly dependent on the quality of the material and cavity, which makes their fabrication challenging. Herein, we demonstrate that cesium lead halide perovskite triangular nanorods fabricated via vapor methods can serve as gain media and effective cavities for multiphoton-pumped lasers. We observed blue-shifts of the lasing modes in the excitation fluence-dependent lasing spectra at increased excitation powers, which fits well with the dynamics of Burstein–Moss shifts caused by the band filling effect. Moreover, efficient multiphoton lasing in CsPbBr₃ nanorods can be realized in a wide excitation wavelength range (700–1,400 nm). The dynamics of multiphoton lasing were investigated by time-resolved photoluminescence spectroscopy, which indicated that an electron–hole plasma is responsible for the multiphoton-pumped lasing. This work could lead to new opportunities and applications for cesium lead halide perovskite nanostructures in frequency upconversion lasing devices and optical interconnect systems.

Low-dimensional semiconductor nanostructures have attracted much interest for applications in integrated photonic and optoelectronic devices. Band gap engineering within single semiconductor nanoribbons helps to manipulate photon behavior in two different cavities (in the width and length directions) and realize new photonic phenomena and applications. In this work, lateral composition-graded semiconductor nanoribbons were grown for the first time through an improved source-moving vapor phase route. Along the width of the nanoribbon, the material can be gradually tuned from pure CdS to a highly Se-doped CdSSe alloy with a corresponding band gap modulation from 2.42 to 1.94 eV. The achieved alloy ribbons are overall high-quality crystals, and the position-dependent band-edge photoluminescence (PL) emission had a peak wavelength continuously tuned from ~515 to ~640 nm. These ribbons can realize multi-color lasing with three groups of lasing modes centered at 519, 557, and 623 nm. It was confirmed that the red lasing was from optical resonance along the length direction, while the green and yellow lasing was from optical resonance along the width direction. These novel nanoribbon structures may be applied to many integrated photonic and optoelectronic devices.