A phototransistor based on a chemical vapor deposited (CVD) MoS2 monolayer exhibits a high photoresponsivity (2200 A W−1) and an excellent photogain (5000). The presence of shallow traps contributes ...to the persistent photoconductivity. Ambient adsorbates act as p‐dopants to MoS2, decreasing the carrier mobility, photoresponsivity, and photogain.
Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic–inorganic hybrid halide ...perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge‐transporting layers have attracted lots of attention due to the photovoltaic and light‐emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non‐polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state‐of‐the‐art strategies on interface‐related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self‐assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.
Rational selection of electrodes plays a critical role in perovskite‐based electronics due to the high reactivity of halide perovskite materials. A comprehensive review of perovskite/electrode interfaces, as well as, state‐of‐the‐art contact engineering, which assists the development of perovskite‐based devices with inhibited interfacial reactions, ohmic carrier transport, and non‐hysteric electronic characteristics, is presented.
Metal‐halide perovskites have drawn profuse attention during the past decade, owing to their excellent electrical and optical properties, facile synthesis, efficient energy conversion, and so on. ...Meanwhile, the development of information storage technologies and digital communications has fueled the demand for novel semiconductor materials. Low‐dimensional perovskites have offered a new force to propel the developments of the memory field due to the excellent physical and electrical properties associated with the reduced dimensionality. In this review, the mechanisms, properties, as well as stability and performance of low‐dimensional perovskite memories, involving both molecular‐level perovskites and structure‐level nanostructures, are comprehensively reviewed. The property–performance correlation is discussed in‐depth, aiming to present effective strategies for designing memory devices based on this new class of high‐performance materials. Finally, the existing challenges and future opportunities are presented.
Low‐dimensional halide perovskites are among the most rapidly emerging building blocks for optoelectronic applications. This review elucidates the advantages and the crucial role of molecular‐/structure‐level low‐dimensional halide perovskites in achieving high performance and enhanced stability in memory applications.
Integrating multiple semiconductors with distinct physical properties is a practical design strategy for realizing novel optoelectronic devices with unprecedented functionalities. In this work, a ...photonic resistive switching (RS) memory is demonstrated based on solution‐processed bilayers of strontium titanate (SrTiO3 or STO) quantum dots (QDs) and all‐inorganic halide perovskite CsPbBr3 (CPB) with an Ag/STO/CPB/Au architecture. Compared with the single‐layer STO or CPB RS device, the double‐layer device shows considerably improved RS performance with a high switching ratio over 105, an endurance of 3000 cycles, and a retention time longer than 2 × 104 s. The formation of heterojunction between STO and CPB significantly enhances the high resistance state, and the separation of the active silver electrode and the CPB layer contributes to the long‐term stability. More importantly, the photonic RS device exhibits UV–visible dual‐band response due to the photogating effect and the light‐induced modification of the heterojunction barrier. Last, tri‐mode operation, i.e., photodetector, memory, and photomemory, is demonstrated via tailoring the light and electric stimuli. This bilayer device architecture provides a unique approach toward enhancing the performance of photoresponsive data‐storage devices.
A solution‐processed photonic memory is fabricated using all‐perovskite SrTiO3/CsPbBr3 bilayers as the switching media. The resistive switching performance of the device is considerably improved compared to the single‐layer counterparts, exhibiting response to dual UV–visible bands, as well as tri‐mode operation of photodetector, memory, and photomemory.
Memristive devices have been extensively demonstrated for applications in nonvolatile memory, computer logic, and biological synapses. Precise control of the conducting paths associated with the ...resistance switching in memristive devices is critical for optimizing their performances including ON/OFF ratios. Here, gate tunability and multidirectional switching can be implemented in memristors for modulating the conducting paths using hexagonal α‐In2Se3, a semiconducting van der Waals ferroelectric material. The planar memristor based on in‐plane (IP) polarization of α‐In2Se3 exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance‐switching ratio. The integration of vertical α‐In2Se3 memristors based on out‐of‐plane (OOP) polarization is demonstrated with a device density of 7.1 × 109 in.−2 and a resistance‐switching ratio of well over 103. A multidirectionally operated α‐In2Se3 memristor is also proposed, enabling the control of the OOP (or IP) resistance state directly by an IP (or OOP) programming pulse, which has not been achieved in other reported memristors. The remarkable behavior and diverse functionalities of these ferroelectric α‐In2Se3 memristors suggest opportunities for future logic circuits and complex neuromorphic computing.
Gate‐tunable and multidirection‐switchable memristive phenomena in a van der Waals ferroelectric α‐In2Se3 are demonstrated. The planar memristor exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance‐switching ratio. A multidirectionally operated α‐In2Se3 memristor is also proposed, enabling the control of the out‐of‐plane (OOP) (or in‐plane (IP)) resistance state directly by an IP (or OOP) programming pulse.
The extraordinary electronic, optical, and mechanical characteristics of 2D materials make them promising candidates for optoelectronics, specifically in infrared (IR) detectors owing to their ...flexible composition and tunable optoelectronic properties. This review presents the recent progress in IR detectors composed of 2D materials and their hybrid structures, including graphene, black phosphorous, transition metal dichalcogenides, halide perovskite as well as other new layered materials and their heterostructures. The focus is on the short‐wave, mid‐wave, and long‐wave infrared regimes, which pose a grand challenge for rational materials and device designs. The dependence of the device performance on the optical and electronic properties of 2D materials is extensively discussed, aiming to present the general strategies for designing optoelectronic devices with optimal performance. Furthermore, the recent results on 2D material‐based heterostructures are presented with an emphasis on the relationship between band alignment, charge transfer, and IR photodetection. Finally, a summary is given as well as the discussion of existing challenges and future directions.
2D materials are among the most rapidly emerging building blocks for high‐performance infrared photodetection. This review elucidates the advantages and the crucial role of 2D materials in achieving high performance and enhanced stability in infrared photodetection, especially in short‐wave, mid‐wave, and long‐wave infrared regimes.
The monolayer transition metal dichalcogenides have recently attracted much attention owing to their potential in valleytronics, flexible and low-power electronics, and optoelectronic devices. Recent ...reports have demonstrated the growth of large-size two-dimensional MoS2 layers by the sulfurization of molybdenum oxides. However, the growth of a transition metal selenide monolayer has still been a challenge. Here we report that the introduction of hydrogen in the reaction chamber helps to activate the selenization of WO3, where large-size WSe2 monolayer flakes or thin films can be successfully grown. The top-gated field-effect transistors based on WSe2 monolayers using ionic gels as the dielectrics exhibit ambipolar characteristics, where the hole and electron mobility values are up to 90 and 7 cm2/Vs, respectively. These films can be transferred onto arbitrary substrates, which may inspire research efforts to explore their properties and applications. The resistor-loaded inverter based on a WSe2 film, with a gain of ∼13, further demonstrates its applicability for logic-circuit integrations.
Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the ...electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices.
Abstract
Monolayer transition metal dichalcogenides, such as MoS
2
and WSe
2
, have been known as direct gap semiconductors and emerged as new optically active materials for novel device ...applications. Here we reexamine their direct gap properties by investigating the strain effects on the photoluminescence of monolayer MoS
2
and WSe
2
. Instead of applying stress, we investigate the strain effects by imaging the direct exciton populations in monolayer WSe
2
–MoS
2
and MoSe
2
–WSe
2
lateral heterojunctions with inherent strain inhomogeneity. We find that unstrained monolayer WSe
2
is actually an indirect gap material, as manifested in the observed photoluminescence intensity–energy correlation, from which the difference between the direct and indirect optical gaps can be extracted by analyzing the exciton thermal populations. Our findings combined with the estimated exciton binding energy further indicate that monolayer WSe
2
exhibits an indirect quasiparticle gap, which has to be reconsidered in further studies for its fundamental properties and device applications.
Atomically thin molybdenum disulfide (MoS(2)) layers have attracted great interest due to their direct-gap property and potential applications in optoelectronics and energy harvesting. Meanwhile, ...they are extremely bendable, promising for applications in flexible electronics. However, the synthetic approach to obtain large-area MoS(2) atomic thin layers is still lacking. Here we report that wafer-scale MoS(2) thin layers can be obtained using MoO(3) thin films as a starting material followed by a two-step thermal process, reduction of MoO(3) at 500 °C in hydrogen and sulfurization at 1000 °C in the presence of sulfur. Spectroscopic, optical and electrical characterizations reveal that these films are polycrystalline and with semiconductor properties. The obtained MoS(2) films are uniform in thickness and easily transferable to arbitrary substrates, which make such films suitable for flexible electronics or optoelectronics.
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