Multimodal Photodiode and Phototransistor Device Based on Two-Dimensional Materials.

Two-dimensional (2D) materials have brought a spectacular revolution in fundamental research and industrial applications due to their unique physical properties of atomically thin thickness, strong light-matter interaction, unity valley polarization and enhanced many-body interactions. To fully explore their exotic physical properties and facilitate potential applications in electronics and optoelectronics, an effective and versatile characterization method is highly demanded. Among the many methods of characterization, optical second harmonic generation (SHG) has attracted broad attention because of its sensitivity, versatility and simplicity. The SHG technique is sufficiently sensitive at the atomic scale and therefore suitable for studies on 2D materials. More importantly, it has the capacity to acquire abundant information ranging from crystallographic, and electronic, to magnetic properties in various 2D materials due to its sensitivity to both spatial-inversion symmetry and time-reversal symmetry. These advantages accompanied by its characteristics of non-invasion and high throughput make SHG a powerful tool for 2D materials. This review summarizes recent experimental developments of SHG applications in 2D materials and also provides an outlook of potential prospects based on SHG.

Most optoelectronic characteristics of two-dimensional (2D) materials are associated with excitonic effects. Excitonic effects in 2D material have been intensively investigated, and various efforts to engineer exciton behavior in 2D materials have been reported for advanced nanophotonic and optoelectronic applications. Excitons in 2D semiconductors can be controlled by external stimuli, including mechanical, electrical, thermal, and magnetic stimuli. Mechanical stimuli applied to a 2D material can generate uniform or non-uniform deformation and strain gradient in the 2D lattice, which creates a strain-induced bandgap energy gradient in the 2D material. In an inhomogeneous bandgap energy gradient generated by a non-uniform strain gradient, excitons drift across the energy gradient. Exciton engineering in deformed 2D materials aims to control exciton movement by mechanical strain. In this snapshot review, we focus on exciton engineering in a mechanically deformed 2D material and their potential towards advanced optoelectronic and photonic applications.

Current state-of-the-art ultraviolet (UV) photodetectors are extensively used in applications ranging from industrial to biomedical science. As a result, there have been consistent efforts to improve their efficiency and to address challenges related to sensitivity and spectral selectivity. Two-dimensional (2D) materials, with their distinct properties, offer a promising solution due to their excellent UV detection characteristics. Additionally, their atomic scalability and CMOS compatibility enable easy integration with flexible platforms and current technologies. The exceptional optoelectronic characteristics, strong light-matter interaction, and quantum confinement in certain 2D materials have led to extensive investigations into 2D material-based UV photodetectors. This review provides a broad overview of the mechanisms of photodetection, various device configurations, and the current progress in both layered and non-layered 2D UV photodetectors. Finally, strategies for improving UV photodetection properties are discussed, along with a future outlook on the integration of 2D UV detectors into commercial platforms.

Two-dimensional (2D) materials with dangling-bond-free surfaces have attracted considerable attention in next-generation electronic applications due to their distinctive properties, such as high carrier mobility, short-channel immunity, and strong light-matter interactions. Recently, various methods have been developed for the preparation of 2D materials, including mechanical exfoliation, chemical vapor deposition, and chemical solution-based processes. Among these, solution processing provides a cost-effective and low-temperature approach for large-scale production. This review highlights recent advancements in solution-processed 2D materials, focusing on preparation methods and their applications in electronic and optoelectronic devices. Additionally, future perspectives are proposed to advance the breakthrough and commercialization of solution technologies for value-added chemical production.

Precision and chip contamination-free placement of two-dimensional (2D) materials is expected to accelerate both the study of fundamental properties and novel device functionality. Current transfer methods of 2D materials onto an arbitrary substrate deploy wet chemistry and viscoelastic stamping. However, these methods produce a) significant cross contamination of the substrate due to the lack of spatial selectivity b) may not be compatible with chemically sensitive device structures, and c) are challenged with respect to spatial alignment. Here, we demonstrate a novel method of transferring 2D materials resembling the functionality known from printing; utilizing a combination of a sharp micro-stamper and viscoelastic polymer, we show precise placement of individual 2D materials resulting in vanishing cross contamination to the substrate. Our 2D printer-method results in an aerial cross contamination improvement of two to three orders of magnitude relative to state-of-the-art dry and direct transfer methods. Moreover, we find that the 2D material quality is preserved in this transfer method. Testing this 2D material printer on taped-out integrated Silicon photonic chips, we find that the micro-stamper stamping transfer does not physically harm the underneath Silicon nanophotonic structures such as waveguides or micro-ring resonators receiving the 2D material. Such accurate and substrate-benign transfer method for 2D materials could be industrialized for rapid device prototyping due to its high time-reduction, accuracy, and contamination-free process.

The integration of two-dimensional (2D) materials with photonic structures has catalyzed a wide spectrum of optical and optoelectronic applications. Conventional nanophotonic structures generally lack efficient reconfigurability and multifunctionality. The atomically thin 2D van der Waals materials can thus infuse new functionality and reconfigurability to the well-established library of photonic structures such as integrated waveguides, optical fibers, photonic crystals, micro-cavities, and metasurface, to name a few. Thanks to the handiness of van der Waals interfaces, the 2D materials can be easily transferred and mixed with other prefabricated photonic templates with high degrees of freedom, and can act as the optical gain, modulation, sensing, or plasmonic media for diverse applications. Here we review recent advents on combining 2D materials to nanophotonic structures for new functionality development or performance enhancements. Challenges and emerging opportunities in integrating van der Waals building blocks beyond 2D materials are also discussed.

With the advent of graphene, two-dimensional (2D) materials have emerged as promising candidates for next-generation electronic and optoelectronic applications. The most anticipated 2D materials have been synthesized and exploited for novel applications. Multilayered zinc chalcogenides (ZnX) are the best precursors for obtaining atomic layer two-dimensional materials by exfoliation. Therefore, we carry out a detailed density functional theory-based study to achieve an exfoliation process of ZnX non-van der Waals sheets by straining and provide a microscopic understanding of the ferroelectric, optic, and spin behaviors of ZnX systems and the corresponding self-healable two-dimensional ZnX devices. The results revealed that 2D ZnX sheets can be obtained when strain is 14% for ZnS and ZnSe, and the peak values of exfoliation energy have a similar order of magnitude to those of traditional 2D materials, indicating the possibility of obtaining 2D ZnX monolayers. For intrinsic 2D ferroelectric materials with in-plane electric polarization, the direction of ZnX sheets can be reversed using an electric field with an energy barrier of ∼0.175 eV per atom for ZnSe, offering a promising functional basis for their application in ferroelectric nanodevices. The first absorption of photons for polarization perpendicular to the monolayer plane occurs in a high energy range of photons, facilitating their application in LEDs. The spin splitting in non-centrosymmetric ZnX crystals exhibits a Rashba spin-texture according to first-principles calculations. The self-healable two-dimensional nanodevices have a smooth curve from -0.5 to 0.5 eV. This work indicates the potential value of non-van der Waals ZnX 2D materials for their application in photoelectric and spintronic nanodevices.

This study presents a comprehensive multi-band analytical and numerical framework to investigate strain-induced topological phase transitions and electronic structure changes in two-dimensional (2D) materials. We derive accurate formulas for strain-dependent band gaps and critical strain thresholds, elucidating the role of strain in band inversion, Berry curvature, and electronic properties in phosphorene and MoS2. These formulas reliably predict topological transitions (e.g., Z2 index or Chern number) and nonlinear band gap reductions, validated by tight-binding simulations, first-principles calculations, and experimental data. The framework is demonstrated for phosphorene and MoS2, with potential extensions to other 2D materials and heterostructures, which may facilitate applications in quantum computing, spintronics, and optoelectronics through strain engineering.

Infrared photodetectors (PDs) are widely used in fields such as military, medical, and aerospace. Traditional semiconductor materials including Si, InGaAs, and HgCdTe show high performance in a wide spectral range with the imaging function. Nevertheless, they also have limitations such as low-temperature operation, high cost, and toxicity. Fortunately, two-dimensional (2D) materials with narrow bandgaps featuring adjustable gaps, mechanical flexibility, and superior optoelectronic properties have the potential to bridge the gap between traditional materials in optoelectronic devices. However, 2D materials’ performance with respect to responsivity (Rλ) and external quantum efficiency (EQE) needs improvement. Tantalum nickel selenium (Ta2NiSe5) with a direct bandgap and high carrier mobility has prospects for broadband PD research. This study combines mechanical exfoliation and micro-nano-processing technology to prepare Ta2NiSe5 nanosheets and design a Ta2NiSe5-based PD, which has a broadband light response from 520 to 1550 nm with an Rλ value of up to 1.07 A/W. The highest EQE of the PD is 2.55, with the lowest noise equivalent power of 2.39 × 10−12 W/Hz1/2 and the highest specific detectivity (D*) of 9.3 × 108 cm Hz1/2/W. The response speed is stable with low power consumption, and the PD can perform high-resolution imaging through different liquids. Hence, Ta2NiSe5-based PDs have photoelectric properties including broadband detection, high responsiveness, and low-light detection, with a broad range of application in new optoelectronics.

This chapter discusses giant optical path length (OPL) from thin-layer molybdenum disulphide originated from their high refractive indices. Refractive optical components rely on the OPL to modify the phase front of an optical beam. It shows that high-index two-dimensional (2D) materials have extraordinary elastic interactions with light, enabled uniquely by the combination of their ultra-thin nature and high refractive indices. 2D layered materials have emerged as promising candidates for miniaturisation of optoelectronic devices, such as photo-detectors, light emitters, absorbers, edge non-linear optics and valleytronic devices, due to their strong inelastic interactions with light. The giant scattering efficiency in high-index 2D materials makes it possible to achieve sophisticated light manipulation based on collective scattering by nanostructured patterns. 2D optical components represents a significant advantage in manufacturing compared to conventional 3D optical components, because different functionalities can all be achieved in a 2D platform sharing the same fabrication processes and this will greatly facilitate large-scale manufacturing and integration.

Recently, nanoscience and technology are based on multidisciplinary fields where electronic and optoelectronic devices have drawn huge attention to overcome the latest development issues. Despite coming from traditional materials, the evolution of low dimensional material, especially two-dimensional semiconductors, became a vibrant candidate for dynamic applications. Monolayer graphene and 2D materials gained a plethora of attention because of their immense electronic and optoelectronic properties, like tunable photon absorption and ultrafast charge transport. These materials, having unique and outstanding properties, bloomed as fascinating contenders with huge potential to explore photonic and optoelectronic applications. The progression of 2D materials toward the comprehension of devices has been one of the auspicious inspirations for the emerging progress of new technology. The main advantage of 2D materials is the modulation of their energy bandgap, which can be implemented in light-related applications. This chapter will focus on the 2D materials and their role in the manufacturing of photonic and optoelectronic devices, such as broadband photodetectors, photovoltaic devices, optoelectronic memory, bio-photonic, light-emitting diode (LED), and MXenes-based photodetectors. Also, a great podium will be provided here to investigate the TMDCs and MXenes for their advantages, challenges, and capabilities to play an important role in future technology.

The post-graphene era is undoubtedly marked by two-dimensional (2D) materials such as quasi-van der Waals antimonene. This emerging material has a fascinating structure, exhibits a pronounced chemical reactivity (in contrast to graphene), possesses outstanding electronic properties and has been postulated for a plethora of applications. However, chemistry and physics of antimonene remain in their infancy, but fortunately recent discoveries have shed light on its unmatched allotropy and rich chemical reactivity offering a myriad of unprecedented possibilities in terms of fundamental studies and applications. Indeed, antimonene can be considered as one of the most appealing post-graphene 2D materials reported to date, since its structure, properties and applications can be chemically engineered from the ground up (both using top-down and bottom-up approaches), offering an unprecedented level of control in the realm of 2D materials. In this review, we provide an in-depth analysis of the recent advances in the synthesis, characterization and applications of antimonene. First, we start with a general introduction to antimonene, and then we focus on its general chemistry, physical properties, characterization and synthetic strategies. We then perform a comprehensive study on the allotropy, the phase transition mechanisms, the oxidation behaviour and chemical functionalization. From a technological point of view, we further discuss the applications recently reported for antimonene in the fields of optoelectronics, catalysis, energy storage, cancer therapy and sensing. Finally, important aspects such as new scalable methodologies or the promising perspectives in biomedicine are discussed, pinpointing antimonene as a cutting-edge material of broad interest for researchers working in chemistry, physics, materials science and biomedicine.

The capability to manipulate the size of the electronic band gap is of importance to semiconductor technology. Among these, a wide direct band gap is particularly helpful in optoelectronic devices due to the efficient utilization of blue and ultraviolet light. Here, we reported a paraffin-enabled compressive folding (PCF) strategy to widen the band gap of two-dimensional (2D) materials. Due to the large thermal expansion coefficient of paraffin, folded 2D materials can be achieved via thermal engineering of the paraffin-assisted transfer process. It can controllably introduce 0.2-1.3% compressive strain onto folded structures depending on the temperature differences and transfer the folding product to both rigid and soft substrates. Exemplified by MoS2, its folded multilayers demonstrated blue-shifts at direct gap transition peaks, six times stronger photoluminescence intensity, almost double mobility, and 20 times higher photoresponsivity over unfolded MoS2. This PCF strategy can attain controllable widening band gap of 2D materials, which will open up novel applications in optoelectronics.

Two-dimensional (2D) materials have attracted increasing interest in the last few years due to their unique morphology and properties and their use in a variety of applications, ranging from electronics to energy storage or catalysis, to name a few. Apart from various well-established 2D materials, such as graphene, h-BN, or MoS2, black phosphorus (BP) has received considerable attention over the last two years because its direct bandgap and his appealing properties for electronic and ultrafast optoelectronic applications. However, its lack of environmental stability severely limits its synthesis and processing. We have recently demonstrated that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions.1 Beyond this success, a more sophisticated chemical modification is highly desirable, like the molecular doping, that is an effective and flexible method towards modulating the electronic properties of 2D materials. Herein, we have developed a chemical route for the non-covalent functionalization of BP with different moieties, including electron-withdrawing organic molecules or tailor-made surfactants.2 Moreover we have extended these concepts towards a new 2D material: antimonene, creating stable suspensions in water and developing its non-covalent functionalization.3 1) D. Hanlon, C. Backes, E. Doherty, C. S. Cucinotta, N. C. Berner, C. Boland, K. Lee, A. Harvey, P. Lynch, Z. Gholamvand, S. F. Zhang, K. P. Wang, G. Moynihan, A. Pokle, Q. M. Ramasse, N. McEvoy, W. J. Blau, J. Wang, G. Abellan, F. Hauke, A. Hirsch, S. Sanvito, D. D. O’Regan, G. S. Duesberg, V. Nicolosi, J. N. Coleman, Nat. Commun. 2015, 6, 8563. 2) G. Abellán, V. Lloret, U. Mundloch, M. Marcia, C. Neiss, A. Görling, M. Varela, F. Hauke, A. Hirsch, Angew. Chem. In. Ed., 2016, 55 (47), 14557. 3) C. Gibaja, D. Rodriguez-San-Miguel, P. Ares, J. Gómez-Herrero, M. Varela, R. Gillen, J. Maultzsch, F. Hauke, A. Hirsch, G. Abellán, F. Zamora, Angew. Chem. In. Ed., 2016, 55 (46), 14345.

Recently, the study of ternary organic solar cells (OSCs) has attracted the efforts of the scientific community, leading to significantly higher performance due to the enhanced harvesting of incoming irradiation. Here, for the first time, and in order to promote this OSC architecture, we review the progress implemented by the application of two-dimensional (2D) materials in the field of blend bulk heterojunction ternary OSCs. Power conversion efficiency (PCE) improvements of the order of 40% compared to the reference binary devices, and PCEs in excess of 8% have been reported by incorporating graphene-based or other 2D materials as a third element inside the active layer. These OSCs combine the synergetic advantages of ternary devices and the superb properties of the 2D material family. In conclusion, the incorporation of the unique properties of graphene and other 2D materials inside the active layer opens up a very promising pathway in the design and construction of high-performance, simply fabricated and low- cost photovoltaic devices.