Polarization-sensitive photodetectors can sense the polarization states of light. Traditional polarization-sensitive photodetectors usually require the incorporation of extra optical components such as polarizers and waveplates, resulting in bulky device and complex structure, which fails to meet the demand for miniaturization of devices. In this work, we have demonstrated linear polarization-sensitive photodetectors based on twisted stacked ReS2/MoSe2 heterojunctions. Due to the formation of built-in electric field caused by the heterojunctions, the photodetectors can achieve optical response under zero bias voltage, with a maximum responsivity of0.17 A/W and a specific detectivity of 6×109 Jones. Meanwhile, photodetectors fabricated by combining two twisted stacked ReS2/MoSe2 heterojunctions can realize detection of arbitrary linear polarized light within a wide wavelength range of 600~800 nm. This study provides a simple method for self-powered linear polarization-sensitive photodetectors.
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Open Access
Issue
The development of emerging technologies, particularly artificial intelligence, has posed significant challenges to traditional computers based on the conventional “von Neumann” architecture, which suffer from high energy consumption and low computing efficiency, making them inadequate for increasingly demanding applications. Neuromorphic computing systems, inspired by the human brain, have emerged as a promising alternative for large-scale, high-density parallel computing owing to their integrated “operation-storage” capability. Brain-like artificial synapses, based on the principles of memristors, are designed to simulate the biological synaptic functions of neurons and provide essential support for neuromorphic computing. In recent years, 2D materials have emerged as promising candidates for brain-like artificial synapses. Among them, transition metal dichalcogenides (TMDs) have been widely used for simulating biological synaptic plasticity owing to their layer-dependent bandgap characteristics, high carrier mobility, and gate voltage-controlled optoelectronic properties.
In this paper, we present innovative experiments on brain-like artificial synapse devices based on three-terminal transistors using TMDs. Single-layer or few-layer WSe2 microflakes of varying thicknesses were obtained through mechanical exfoliation, while oxygen plasma treatment was applied to the SiO2/Si substrate surface to enable interfacial state tuning. The dry transfer technique was then applied to fabricate brain-like artificial synapse devices based on WSe2 materials, followed by an annealing process at 300 ℃ under an argon gas atmosphere. Optical and scanning electron microscopy were employed to characterize the morphology and thickness of the WSe2 material. To analyze the electrical properties of the devices, the transfer and I–V output curves were measured. The post-synaptic current (PSC) as a function of pulse number was evaluated under two conditions: 50 continuous cycles of a 50 V pulse and 50 cycles of a −10 V/−50 V pulse. Both measurements were conducted under the same test conditions, with a source-drain voltage of 3 V, a pulse duration of 30 ms, and a pulse period of 60 ms to assess the stability of the artificial synapse devices. Furthermore, the biological synaptic plasticity of the artificial synapse devices can be tuned by varying the duration of oxygen plasma treatment (10 s, 60 s, 120 s, and 180 s) on the surface of the SiO2/Si substrate, thereby modifying the interfacial state density.
The results demonstrated that by controlling the gate voltage polarity, a transition from high-resistance states to low-resistance states can be achieved. The PSC at 0 V gate voltage after the application of a 50 V gate voltage pulse was greater than that observed after the application of a −10 V gate voltage pulse. Under a 50 V gate voltage, the device entered a low-resistance state, whereas under a −10 V gate voltage, the device remained in a high-resistance state, successfully enabling switching between high- and low-resistance states. During the long-term potentiation phase, the PSC of devices subjected to different plasma treatment durations continuously increases with the number of pulses. Moreover, as the number of pulses increases, the PSC exhibits a gradual saturation trend, which becomes more pronounced with longer treatment times. In contrast, during the long-term depression phase, the PSC decreases as the number of pulses increases, highlighting the effect of plasma treatment duration on biological synaptic function.
This paper presents an innovative experiment on brain-inspired artificial synapses based on transition metal dichalcogenide tungsten diselenide (WSe2) transistors. The study encompasses device fabrication, characterization, and property measurement, integrating research with practical teaching. This approach not only fosters students’ interest but also helps cultivate their creativity and problem-solving abilities.
Experimental teaching plays an important role in cultivation of talents in college, how to incorporate scientific research into experimental teaching is the key for creativity training of undergraduates. In information era, various data types and the vast increase of data storage increase the requirement of memory with high performance. Memory devices based on transition metal sulfides have become a research hotspot in the field of memory due to their good storage capacity and high integration density. Therefore, an innovative research experiment of memory based on transitional metal sulfides WS2 memory is designed in this paper. Mechanical peeling and dry transfer are used to fabricate field effect transistor (FET) devices based on WS2. Raman spectra is used for WS2 material characterization. Oxygen plasma treatment is employed to treat the surface of SiO2 by interface engineering to realize multistate memory, which is followed by electrical and memory property measurements. This innovative experiment covers contents from material characterization, memory device fabrication, electrical and memory property measurement and the mechanism to achieve memory and so on, which is not only related to semiconductor, material science, microelectronics and integrated circuits, also incorporated real research content, and thus can enhance the research enthusiasm of undergraduates and further cultivate their scientific and innovative capabilities.
Open Access
Topical Review
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Two-dimensional (2D)/quasi-2D organic-inorganic halide perovskites are regarded as naturally formed multiple quantum wells with inorganic layers isolated by long organic chains, which exhibit layered structure, large exciton binding energy, strong nonlinear optical effect, tunable bandgap via changing the layer number or chemical composition, improved environmental stability, and excellent optoelectronic properties. The extensive choice of long organic chains endows 2D/quasi-2D perovskites with tunable electron-phonon coupling strength, chirality, or ferroelectricity properties. In particular, the layered nature of 2D/quasi-2D perovskites allows us to exfoliate them to thin plates to integrate with other materials to form heterostructures, the fundamental structural units for optoelectronic devices, which would greatly extend the functionalities in view of the diversity of 2D/quasi-2D perovskites. In this paper, the recent achievements of 2D/quasi-2D perovskite-based heterostructures are reviewed. First, the structure and physical properties of 2D/quasi-2D perovskites are introduced. We then discuss the construction and characterizations of 2D/quasi-2D perovskite-based heterostructures and highlight the prominent optical properties of the constructed heterostructures. Further, the potential applications of 2D/quasi-2D perovskite-based heterostructures in photovoltaic devices, light emitting devices, photodetectors/phototransistors, and valleytronic devices are demonstrated. Finally, we summarize the current challenges and propose further research directions in the field of 2D/quasi-2D perovskite-based heterostructures.
Owing to their excellent optoelectronic properties, halide perovskite is very promising for photodetectors and other optoelectronic devices. Perovskite heterostructures are considered to be the key components for these devices. However, it is challenging to rationally synthesize those heterostructures. Here, we demonstrate that perovskite can be epitaxially grown on PbS by vapor transport, thereby creating an interesting CsPbBr3-PbS heterostructure. Remarkably, photodetectors based on CsPbBr3-PbS heterostructures exhibit visible to infrared broadband response with room temperature operation up to 2 μm. The room temperature detectivity higher than 1.0 × 109 Jones was obtained in the 1.8- to 2-μm range. Furthermore, the p-n heterojunction exhibits a clear rectifying characteristic and enables detector to operate at zero-bias. Our study provides fundamentally contributes to establish the epitaxial growth perovskite heterostructures and demonstrate a materials platform for efficient perovskite-based optoelectronic devices.
The optoelectronic performances of the layered materials are strongly dependent on the thickness of the samples due to the surface effect. As the size of the samples decreases to few nanometers, the surface depletion field and surface defect density are prominent arising from the large surface to volume ratio. For instance, thin two-dimensional (2D) organic-inorganic hybrid perovskite microplates usually exhibit a rather low photoluminescence quantum yield (PLQY), owning to the strong surface effect. Here, we report that the PLQY can be enhanced as large as 28 times in (iso-BA)2PbI4 (BA = C4H9NH3) 2D perovskite thin microplates encapsulated by graphene, resulting in that the PLQY is more than 18% for the microplate with a thickness of 6.7 nm at 78 K. As the thickness of the 2D perovskite microplate increases, the enhancement is gradually reduced and finally vanishes. This observation is in striking contrast to that in monolayer transition metal dichalcogenides (TMDs), when the PLQY is quenched by covering a layer of graphene due to the efficient charge transfer. The enhancement of PLQY in 2D perovskites can be mainly ascribed to the reduced quantum confined Stark effect (QCSE) due to the reduced surface depletion field after covering graphene flake, resulting in the enhanced radiative recombination efficiency. Our findings provide a cost-effective approach to enhance the luminescence, which may pave the way toward high performance light emitting devices based on 2D perovskites.
Surface depletion field would introduce the depletion region near surface and thus could significantly alter the optical, electronic and optoelectronic properties of the materials, especially low-dimensional materials. Two-dimensional (2D) organic—inorganic hybrid perovskites with van der Waals bonds in the out-of-plane direction are expected to have less influence from the surface depletion field; nevertheless, studies on this remain elusive. Here we report on how the surface depletion field affects the structural phase transition, quantum confinement and Stark effect in 2D (BA)2PbI4 perovskite microplates by the thickness-, temperature- and power-dependent photoluminescence (PL) spectroscopy. Power dependent PL studies suggest that high-temperature phase (HTP) and low-temperature phase (LTP) can coexist in a wider temperature range depending on the thickness of the 2D perovskite microplates. With the decrease of the microplate thickness, the structural phase transition temperature first gradually decreases and then increases below 25 nm, in striking contrast to the conventional size dependent structural phase transition. Based on the thickness evolution of the emission peaks for both high-temperature phase and low-temperature phase, the anomalous size dependent phase transition could probably be ascribed to the surface depletion field and the surface energy difference between polymorphs. This explanation was further supported by the temperature dependent PL studies of the suspended microplates and encapsulated microplates with graphene and boron nitride flakes. Along with the thickness dependent phase transition, the emission energies of free excitons for both HTP and LTP with thickness can be ascribed to the surface depletion induced confinement and Stark effect.
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