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Mixed dimensional van der Waals heterostructure based on layered two-dimensional molybdenum disulfide (MoS2) interfaced to gallium nitride (GaN) has attracted tremendous attention due to its unique properties and application in novel electronic, optoelectronic, and quantum devices. However, developing facile synthesis methods and insights into the exciton dynamics for this system still remains a major challenge. Here, a simple and cost-effective method is demonstrated for large-scale synthesis of monolayer MoS2 on differently doped GaN substrates. A mixed aqueous solution of Na2MoO4 and NaOH is spin-coated on GaN and sulfurated in one step by chemical vapor deposition (CVD). High quality monolayer MoS2 nanosheets with side length over 400 μm and surface coverage ratio of more than 90 % are achieved on GaN. Furthermore, the PL intensity, excitonic transition ratios and ultrafast exciton dynamics of MoS2 are observed to be largely modulated by the doping type of GaN, owing to substrate-induced doping, which is proved by Raman, PL and transient absorption spectroscopy. Notably, p-GaN can attract electrons from monolayer MoS2 and weaken its intrinsic n-doping, thereby facilitating higher PL intensity as well as longer exciton lifetime, while n-GaN provides strong n-doping and generates opposite effect. This work hereby presents a pathway for large-scale synthesis of MoS2/GaN heterostructures and further understanding of their charge transfer properties and exciton dynamics, which should inspire their applications for optoelectronic devices.

The extraordinary mechanical compliance of 2D molybdenum disulfide (MoS2) makes it an ideal candidate for strain modulation of various electrical and optical properties. However, developing facile methods for accurate and stable engineering of strain still remains a major challenge. Here, a novel and effective method is demonstrated for introducing periodic strain into monolayer MoS2 by direct growth on nano‐patterned sapphire substrates (NPSS). A mixed aqueous solution of Na2MoO4 and NaOH is spin‐coated on the NPSS and sulfurated in one step by chemical vapor deposition (CVD). Highly oriented monolayer MoS2 single‐crystal nanosheets with high quality and few sulfur vacancies are achieved conformally on the NPSS via a liquid‐mediated growth mode. Notably, the periodically distributed blue shift of the PL emission peak demonstrated periodic compressive strain is introduced into the nano‐patterned MoS2 via the thermal expansion difference between MoS2 and substrates. Furthermore, photodetectors fabricated using the nano‐patterned monolayer MoS2 exhibit a high photo‐to‐dark current ratio (PDCR) over 106, an excellent detectivity of 5.4 × 1013 Jones, and a fast photoresponse of 7.7 ms, owing to the strain‐induced back‐to‐back built‐in electric field, enhanced light absorption by light‐scattering effect and fewer S vacancy defects. The scanning imaging demonstration based on the single‐pixel nano‐patterned MoS2 photodetector further confirms its great potential in image sensors. This work hereby presents a pathway for direct conformal growth of nano‐patterned monolayer MoS2 with precisely periodic strain, which should inspire the applications for high‐performance optoelectronic devices via the strategy of patterned substrate engineering by the periodic nanostructures. [ABSTRACT FROM AUTHOR]

The increasing demand for multispectral information acquisition and the complexity of application environments have sparked a growing interest in broadband detection. However, achieving a high level of responsivity across a wide response range remains a significant challenge. Herein, an ultrasensitive broadband phototransistor based on hybrid photogating (HPG) structure is demonstrated, which consisted of a quasi‐2D beta‐phase gallium oxide (β‐Ga2O3) nanoflake as the carrier transport channel and a tellurium (Te) nanoflake as the photogating layer. Attributed to the strong doping influence of the Te nanoflake, a low off‐state current of pA level and a high on/off current ratio of ≈108 are obtained. Upon 255 nm wavelength illumination, the device exhibited an ultrahigh responsivity up to 3.82 × 106 A W−1 and a detectivity as high as 1.59 × 1014 Jones across a large gate voltage range. Notably, an exciting infrared response is obtained with a responsivity of 138 A W−1 and a detectivity of 3.70 × 109 Jones under the 1550 nm wavelength illumination, exclusively achievable when the gate voltage exceeded 4 V. Leveraging the gate‐tunable spectral response, an innovative model for secure optical communication was proposed. This work presents an efficient and feasible strategy for fabricating multifunctional optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this article, a photodetector (PD) based on nanoporous (NP) AlGaO/AlGaN with efficient light capture and enhanced shortwave deep-UV (DUV) response has been demonstrated. A controllable electrochemical etching was utilized to obtain the NP-AlGaN with an extremely low reflectivity and a strong coupling absorption. After thermal oxidation, the NP-AlGaN was converted into NP-AlGaO, which can significantly suppress the dark current for the fabricated PD, resulting in a detectivity of up to 1.5 × 1013 Jones at 5 V. Meanwhile, defect passivation during oxidation significantly enhances its response speed (6–7 μs), contributing to a high gain-bandwidth product of 2.6 × 105. Critically, the NP-AlGaO/AlGaN hybrid structure greatly improves the responsivity for the shortwave DUV band and the high penetration confers the PD with even better detection capability in the wider DUV band. Therefore, the proposed device manipulating photon motion by means of novel nano-optical structures has great prospects for the detection of weak optical signals in the wide DUV spectral range, also opening up great opportunities for high-sensitivity sensors based on the nanostructured semiconductors. [ABSTRACT FROM AUTHOR]

Mixed dimensional van der Waals heterostructure based on layered two-dimensional molybdenum disulfide (MoS2) interfaced to gallium nitride (GaN) has attracted tremendous attention due to its unique properties and application in novel electronic, optoelectronic, and quantum devices. However, developing facile synthesis methods and insights into the exciton dynamics for this system still remains a major challenge. Here, a simple and cost-effective method is demonstrated for large-scale synthesis of monolayer MoS2 on differently doped GaN substrates. A mixed aqueous solution of Na2MoO4 and NaOH is spin-coated on GaN and sulfurated in one step by chemical vapor deposition (CVD). High quality monolayer MoS2 nanosheets with side length over 400 μm and surface coverage ratio of more than 90 % are achieved on GaN. Furthermore, the PL intensity, excitonic transition ratios and ultrafast exciton dynamics of MoS2 are observed to be largely modulated by the doping type of GaN, owing to substrate-induced doping, which is proved by Raman, PL and transient absorption spectroscopy. Notably, p-GaN can attract electrons from monolayer MoS2 and weaken its intrinsic n-doping, thereby facilitating higher PL intensity as well as longer exciton lifetime, while n-GaN provides strong n-doping and generates opposite effect. This work hereby presents a pathway for large-scale synthesis of MoS2/GaN heterostructures and further understanding of their charge transfer properties and exciton dynamics, which should inspire their applications for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Broadband detection technology is crucial in the fields of astronomy and environmental surveying. Two dimensional (2D) materials have emerged as promising candidates for next-generation broadband photodetectors with the characteristics of high integration, multi-dimensional sensing, and low power consumption. Among these, 2D tellurium (Te) is particularly noteworthy due to its excellent mobility, tunable bandgap, and air stability. However, the performance of the Te-based photodetector has been hindered by high dark current and cut-off wavelength limitations associated with its intrinsic bandgap. Here, the Te / bismuth selenide (Bi 2 Se 3 ) van der Waals (vdWs) p-n heterojunction with a clean interface and type-II band alignment, designed to address these challenges are presented. The Te/Bi 2 Se 3 heterojunction photodetectors demonstrate an ultra-broadband photodetection range from Ultraviolet (UV) to Mid-infrared (MIR) (365 nm-4.3 µm) and a high responsivity up to 880 mA W -1 at 1550 nm under zero bias. Moreover, benefiting from the anisotropy crystal structure of Te, the photodetector shows an obvious polarization-sensitive photoresponse and enormous potential in optical communication and polarization imaging. This work hereby provides significant insight into low-powered, high-performance, and broadband vdWs heterojunction photodetectors and their functional applications., (© 2024 Wiley‐VCH GmbH.)

Modulating the electrical properties of two-dimensional (2D) materials is a fundamental prerequisite for their development to advanced electronic and optoelectronic devices. Substitutional doping has been demonstrated as an effective method for tuning the band structure in monolayer 2D materials. Here, we demonstrate a facile selective-area growth of vanadium-doped molybdenum disulfide (V-doped MoS 2 ) flakes via pre-patterned vanadium-metal-assisted chemical vapor deposition (CVD). Optical microscopy characterization revealed the presence of flake arrays. Transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were employed to identify the chemical composition and crystalline structure of as-grown flakes. Electrical measurements indicated a light p-type conduction behavior in monolayer V-doped MoS 2 . Furthermore, the response time of phototransistors based on V-doped MoS 2 monolayers exhibited a remarkable capability of 3 ms, representing approximately 3 orders of magnitude faster response than that observed in pure MoS 2 phototransistors. This work hereby provides a feasible approach to doping of 2D materials, promising a scalable pathway for the integration of these materials into emerging electronic and optoelectronic devices.

Motivated by the goals of fabricating highly reliable, high performance, and cost-efficient self-powered photodetector (PD) for numerous scientific research and civil fields, an organic-inorganic hybrid solar-blind ultraviolet (UV) PD based on PEDOT: PSS/exfoliated β-Ga 2 O 3 microwire heterojunction was fabricated by a flexible and cost-effective assembly method. Benefiting from the heterojunction constructed by the highly crystalline β-Ga 2 O 3 and the excellent hole transport layer PEDOT: PSS, the device presents a high responsivity of 39.8 mA/W at 250 nm and a sharp cut-off edge at 280 nm without any power supply. Additionally, the ultra-high normalized photo-to-dark current ratio (> 10 4 mW -1 cm 2 ) under reverse bias and the superior detectivity of 2.4×10 12 Jones at zero bias demonstrate the excellent detection capabilities. Furthermore, the hybrid PD exhibits a rapid rise time (several milliseconds) and high rejection ratio (R 250 /R 365 : 5.8 × 10 3 ), which further highlights its good spectral selectivity for solar-blind UV. The prominent performance is mainly ascribed to the efficient separation of the photogenerated carriers by the large built-in electric field of the advanced heterojunction. This flexible assembly strategy for solar-blind UV PD combines the advantages of high efficiency, low cost and high performance, providing more potential for PD investigation and application in the future.