Two-dimensional (2D) materials have attracted great research interest owing to their remarkable properties and promising application in electronic and optoelectronic devices. However, modulating the electrical conduction feature of 2D materials to match the basic requirements for constructing various functional devices is still a big challenge. Herein, we report the conduction feature modulation and device application of nonlayered 2D MnS nanosheets synthesized via chemical vapor deposition (CVD). By precisely tuning the growth temperature from 500 to 710 °C, the thickness of MnS nanosheets can be continuously modulated from ~3.5 to ~118.8 nm with the grain size changing from ~5 to ~27 μm. The as-grown MnS nanosheets possess uniform triangle morphology with high crystallinity and strong second-order nonlinear optical properties. Field-effect transistors based on MnS nanosheets exhibit an interesting conduction feature transition from p-type semiconductor to metal as the thickness increasing from thinner to thick. As results, the photodetector based on thinner MnS semiconductor achieves superior photoresponsivity of 20.47 A/W, high detectivity of 5.31×1010 Jones, and relative fast response time of 180 ms. Our findings not only enrich the family of intrinsic p-type 2D materials but also open a new avenue for electrical property engineering in non-layered 2D materials.
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HgCdTe avalanche photodiodes (APDs) are promising for mid-wave infrared weak-signal detection because electron-initiated avalanche multiplication can provide high gain with low excess noise. However, conventional PIN HgCdTe APDs still suffer from the trade-off between avalanche gain and dark current, especially under high reverse bias, where band-to-band tunneling and hot-carrier transport become significant. In this work, we combine experimental characterization and physics-based simulation to investigate this limitation. The temperature-dependent dark-current characteristics of reference PIN HgCdTe APDs are measured and reproduced using a calibrated device model incorporating recombination, tunneling, and avalanche processes. The agreement between experiment and simulation provides a reliable basis for analyzing dominant dark-current mechanisms and guiding device-structure optimization. Based on this experimentally calibrated framework, we propose a band-engineered n-v-π-B-p HgCdTe APD with redistributed electric field and an embedded barrier layer to suppress unfavorable carrier transport. Simulations predict that the proposed structure achieves higher gain at a given dark current than the conventional PIN design, with gains on the order of 104 at 77 K and 102 at 150 K. These results suggest that experimentally grounded band and field engineering is a promising route toward weak-signal MWIR signal detection.
We demonstrate a significant light-triggered current enhancement in SiC bipolar PIN diodes through ultraviolet (UV) light injection, achieving a 2.74× current gain at 3.5 V under 365 nm illumination. By integrating an optical window for targeted photon injection into the intrinsic region, UV-generated electron−hole pairs enhance conductivity modulation and lower the forward voltage drop. Crucially, we reveal a pronounced structural dependence: vertical devices outperform lateral counterparts due to more effective utilization of photogenerated carriers. This advantage stems from shorter carrier transport path of the vertical architecture and reduced surface recombination losses, whereas lateral devices suffer from enhanced carrier recombination due to surface-parallel carrier drift. This study establishes UV illumination as a scalable and non-invasive strategy for dynamic performance tuning of SiC bipolar devices, bypassing complex lifetime-enhancement processes while enabling adaptive conduction for smart power systems.
Synaptic devices are required to break the Von Neumann bottleneck by incorporating memory and processing within the same physical location and hence improve the computational strength for artificial intelligence and the Internet of Things (IoT). In this article, we report the synaptic characteristics of a two-terminal device, where an organic semiconductor (OSC) N, N'–dioctyl–3,4,9,10–perylenedicarboximide (PTCDI–C8) is sandwiched between Indium tin oxide (ITO) and gold (Au) on a silicon/silicon–dioxide (Si/SiO2) substrate, under multi-stimulus activation. The synaptic device utilizes a tungsten lamp that emits a broad spectral range from ultraviolet (UV) to infrared (IR) as a pre-synaptic signal, while providing a change in current as a post-synaptic signal. We demonstrate the short-term plasticity (STP) and long-term plasticity (LTP) based on exposure time. Electron–hole pairs are generated in OSC when UV–visible light is absorbed from external stimulation, which triggers the output current, whereas the IR component introduces a thermally assisted contribution that further enhances charge transport. Hence, the effect of temperature is also observed, which simultaneously acts as an external stimulation for the synaptic device. Under temperature accompanied by optical stimulation, the learning-forgetting-relearning phenomenon is also achieved in this work. Additionally, logic operation and associative learning phenomena are demonstrated by the device under IR and tungsten source. The change in current depends on the exposure time and the temperature generated on the surface. Since temperatures above 45 °C are hazardous to human beings, this synaptic device is useful in measuring and retaining this information. The incorporation of temperature with light is not commonly used as an external synaptic stimulus in the same device, hence it can find its applications in neuromorphic computing and artificial sensory neuron systems, which is also capable of sensing and retaining thermal information.
Two-dimensional (2D) van der Waals (vdW) materials offer atomically thin, dangling-bond-free interfaces and strong electrostatic control characteristics, enabling a new paradigm for optoelectronic devices. This review focuses on vdW contact engineering and heterostructure construction. The vdW contact can suppress Fermi-level pinning, reduce contact resistance, and preserve the intrinsic properties of 2D semiconductors. Leveraging such clean interfaces, 2D vdW materials show great potential in implementing functional devices, including photodetectors, miniaturized computational spectrometers, reconfigurable devices, and neuromorphic systems. In these cases, the tunable vdW interfaces eliminate lattice-matching constraints and allow feasible heterogeneous integration. This review discusses the recent progress and future prospects in this field, providing guidance for realizing functional applications based on vdW device configuration.
Ga2O3 is a leading candidate for next-generation high-power electronics and deep-ultraviolet optoelectronics due to its ultrawide bandgap and high theoretical breakdown field. While the stable β-phase has been extensively studied, interest is shifting toward metastable polymorphs to broaden functionality. Among these, the ε/κ phase is distinguished by its non-centrosymmetric orthorhombic structure, offering unique ferroelectric and piezoelectric properties. Despite progress in epitaxial stabilization, a comprehensive understanding of its crystal structure, physical behavior, and device potential remains limited. This review critically examines the ε−κ phase relationship and heteroepitaxial growth mechanisms on Al2O3, GaN, and other substrates, highlighting the roles of supersaturation, doping, and buffer layer engineering in stabilizing metastable phases while suppressing secondary phases. Furthermore, the work explores the unique physical properties of ε/κ-Ga2O3, including the substantial spontaneous polarization, a large piezoelectric coefficient, and the direct-bandgap nature favorable for DUV detection. The practical efficacy of these attributes is showcased across a diverse technological portfolio, including ferroelectric memristors for neuromorphic computing, high-frequency acoustic wave resonators, and high-sensitivity solar-blind photodetectors. Finally, the review identifies remaining challenges-such as rotational domain mitigation and polarization saturation-providing a strategic roadmap for realizing multifunctional ε/κ-Ga2O3-based devices.
Optical detectors based on metal oxide semiconductor thin films have always been a research hotspot in the field of optoelectronic detection due to their advantages of simple structure and convenient preparation. However, due to the characteristics of the material itself and the inherent working mechanism of the device, these devices often have their own shortcomings. In this work, Eu doped BaTiO3 thin film was introduced as a buffer layer to enhance the performance of photoconductive detector based on ZnO thin film. Compared with the un-doped BaTiO3 buffer layer, the Eu:BTO buffer layer can further enhance the photodetection performance of detector based on ZnO film. The detector on Eu:BTO buffer layer exhibits larger photocurrent (450 nA) and smaller dark current (1.01 nA) compared with that on un-doped BTO buffer layer (100 and 10 nA), leading to larger on/off ratio. Meanwhile, the response speed of the device can reach 0.51 and 1.04 s, respectively, which is much superior than the device based on original ZnO film (10.55 and 14.98 s). At the appropriate doping concentration (1% Eu:BTO), the increased polarization electric field is the main reason for achieving performance enhancement.
The crystallization kinetics of wide-bandgap perovskite thin films inevitably generate abundant defects at grain boundaries and surfaces, which act as non-radiative recombination centers and degradation initiation sites. Here, we introduce 3,5-bis(trifluoromethyl)aniline as an additive into the precursor solution. It promotes grain growth, improves grain quality, chemically passivates defects to reduce non-radiative recombination. Meanwhile, hydrophobic fluorine groups form a moisture-repellent barrier. The optimized perovskite/silicon tandem solar cell achieves a champion efficiency of 32.70%. After 500 h of maximum power point tracking under illumination at room temperature in N2 atmosphere, the unencapsulated device retains 91% of its initial power conversion efficiency (PCE), significantly higher than that of the control device (72%), demonstrating excellent operational stability. This additive engineering offers an effective strategy to boost both efficiency and stability in perovskite/silicon tandem solar cells.
Bismuth sulfide (Bi2S3), a widely studied photocatalytic material, has attracted increasing interest for optoelectronic applications because of its strong light absorption and suitable bandgap. However, the photoelectric properties of single-crystalline Bi2S3 remain insufficiently explored, mainly due to the difficulty in synthesizing high-quality ultrathin crystals suitable for device integration. Here, we report the low-pressure chemical vapor deposition (LPCVD) growth of ultrathin single-crystalline Bi2S3 nanosheets with thicknesses of approximately 40–60 nm and demonstrate high-performance gate-tunable photodetectors based on back-gated field-effect transistor (FET) devices. Under 630 nm illumination, the devices deliver a high responsivity of 67.36 A·W−1, an external quantum efficiency (EQE) of 52618%, and a detectivity on the order of 1012 Jones. These metrics outperform previously reported Bi2S3 photodetection devices and highlight the great potential of LPCVD-grown Bi2S3 for high-speed and high-sensitivity photodetection. Combined with its tunable bandgap and structural anisotropy, Bi2S3 represents a promising material platform for next-generation photodetectors, image sensors and integrated optoelectronic technologies.
This work demonstrates high-performance quasi-vertical GaN Schottky barrier diodes (SBDs) on sapphire substrates utilizing a regrown p-GaN sidewall structure. The regrown p-GaN sidewall alleviates electric-field crowding at the Schottky-contact edge and suppresses sidewall-associated reverse leakage, leading to a dramatic enhancement in breakdown voltage (BV) from 71 to 847 V. Furthermore, the reverse leakage current density is suppressed by five orders of magnitude, decreasing from 0.29 to 5.2 × 10−6 A/cm2 at a cathode bias of −50 V. Two-dimensional TCAD simulations were performed to verify the field-modulation effect of the p-GaN sidewall. The quasi-vertical SBDs with p-GaN sidewall demonstrate robust stability under both thermal and reverse-bias stress, highlighting the potential of regrown sidewall architectures for the next generation of GaN-on-sapphire power electronics.
In the readout circuit of micro-electromechanical systems (MEMS) microphones, the high-voltage pins of charge pumps necessitate electrostatic discharge (ESD) protection designs featuring high holding voltage and high-temperature tolerance. Traditional ESD solutions cannot effectively meet the requirement. Accordingly, this paper proposes a parallel dual-BJT enhanced silicon-controlled rectifier (DBESCR) structure, which is verified in a 0.18 µm Bipolar-CMOS-DMOS (BCD) process. By incorporating a parallel dual-BJT shunt design based on the low-voltage-triggered silicon-controlled rectifier (LVTSCR), the holding voltage is effectively enhanced without a significant increase in chip area. Transmission line pulse (TLP) test results demonstrate that the DBESCR device achieves a trigger voltage of 11.8 V and a high holding voltage of 9.69 V. At an elevated temperature of 75 °C, the structure maintains a picoamperes-level leakage current, and the ESD performance of the device does not degrade noticeably. The proposed DBESCR fully meets the 9 V ESD protection design requirements for charge pumps in MEMS microphone readout circuits and exhibits ESD robustness exceeding 8 kV under the human body model (HBM).
AlGaN/GaN-based Schottky barrier diodes grown on Si substrates with n-GaN/p-NiO/n-GaN lateral junctions are proposed and fabricated. The n-GaN/p-NiO/n-GaN lateral junctions effectively extend the depletion region in the GaN drift layer. The more homogenized electric field reduces the electric field magnitude near both the Schottky contact and the field plate (FP) edge. Consequently, the fabricated lateral power device achieves a breakdown voltage (BV) of ~1.6 kV and yields a high Baliga’s figure of merit (BFOM) of ~1.47 GW·cm−2. The n-GaN/p-NiO/n-GaN lateral junctions also contribute to suppressing the electron trapping effect and reducing the dynamic specific on-resistance (Ron,sp) by 1.5 times. With the developed physical models, we have also investigated the impact of different p-NiO designs on the blocking effect for the proposed device. We report that the n-GaN layer in the n-GaN/p-NiO/n-GaN lateral junctions shall be effectively depleted so that AlGaN/GaN-based Schottky barrier diodes with high BV can be achieved.
Achieving simultaneous phase stabilization and ultralow leakage remains a fundamental challenge for ZrO2-based high-k dielectrics. This work demonstrates high-performance 5.7 nm ZrO2-based metal−insulator−metal capacitors through coordinated interfacial engineering and defect passivation. The AlZrO alloy interfacial layer preserves lattice coherence and provides an interfacial barrier while stabilizing the anti-ferroelectric tetragonal phase ZrO2, enabling an equivalent oxide thickness of 0.89 nm. Subsequent in-situ remote O2 plasma treatment passivates oxygen vacancies via radical oxidation without inducing plasma damage. As a result, the capacitors achieve an ultralow leakage current density of 3 × 10−10 A/cm2 at 1 V, a breakdown voltage exceeding 5 V, and a projected 10-year operating voltage above 2.4 V based on time-dependent dielectric breakdown extrapolation. All processes are conducted below 350 °C, ensuring back-end-of-line (BEOL) compatibility. These results demonstrate a pathway toward simultaneous dielectric constant enhancement, leakage suppression, and long-term reliability in ultrathin ZrO2-based high-k dielectrics.
Low-dimensional metal-halide perovskites have emerged as promising materials for optoelectronic synapses and neuromorphic vision systems owing to their strong light–matter interactions, tunable optoelectronic properties, and mixed ionic–electronic transport. Compared with three-dimensional counterparts, low-dimensional perovskites exhibit more powerful control over charge transport, ion migration, and optical absorption with enhanced stability. In this review, we outline the composition, dimensionality, and growth strategies of low-dimensional perovskites, emphasizing how structural engineering governs their optical and electrical properties. Their photodetection, memristive, and photo-reservoir behaviors are further discussed to form physical foundation for light-stimulated synaptic functions, including optical sensing, memory retention, and conductance modulation. We review representative optoelectronic synapses based on 0D, 1D, and 2D perovskites according to their device-level mechanisms, highlighting how dimensionality enables distinct visual functions and device architectures. Exemplary neuromorphic algorithms are discussed as well, including artificial neural networks, convolutional neural networks, spiking neural networks, recurrent neural networks, and reservoir computing, which translate perovskite synaptic responses into higher-level capabilities such as image recognition, multimodal perception, and motion detection. Finally, we catalog the remaining challenges including lead toxicity, limited lead-free performance, crystallization and device-to-device variations, ion-migration-induced instability, and options for wafer-scale patterning and addressable integration. By connecting materials design, synaptic device physics, neuromorphic algorithms, and scalable integration strategies, with perspectives on how low-dimensional perovskites can evolve from laboratory-scale optoelectronic synapses into practical platforms for next-generation artificial vision systems.
van der Waals (vdW) heterojunctions possess great potential for next-generation high-performance optoelectronic devices owing to their facile fabrication and high-quality interfaces. In this study, GeS/MoS2 vdW heterojunction photodetectors were fabricated and investigated. After suppressing electron recombination by eliminating the non-heterojunction regions on the GeS side, the devices exhibited pronounced rectifying behavior. A large rectification ratio of 2.4 × 103 and an ideality factor of 2.3 were achieved. Furthermore, the devices demonstrated photovoltaic-type photodetection performance, including a responsivity of 10.6 mA/W, fast rise/decay time of 83 ms/98 ms, respectively. Notably, the responsivity was further improved to 291.5 mA/W under modulation of Vg. These results provide valuable insights into the optimization and development of high-performance optoelectronic devices based on two-dimensional materials and vdW heterojunctions.
Mid-infrared light beyond 4 μm carries molecular vibrational fingerprints that are essential for gas sensing, emission monitoring and thermal-scene perception. Existing infrared systems still rely on full-frame acquisition, data conversion, transmission and back-end computation. This architecture is increasingly inefficient for distributed and mobile sensing, where power, latency and bandwidth are strictly constrained. Here we report a reconfigurable mid-infrared photodetector based on a b-As0.3P0.7/MoS2 van der Waals(vdWs) heterojunction. The narrow-bandgap b-As0.3P0.7 layer enables broadband detection from 520 nm to 4.05 μm, while the gate-tunable heterointerface reconfigures carrier separation and transport. The device produces 15 switchable photocurrent states and exhibits a response time on the order of hundreds of microseconds. We further perform hardware-aware infrared image-classification simulations, achieving a mean test accuracy of 86.75%. These results highlight the potential of reconfigurable vdW heterojunctions as programmable infrared sensing elements for future edge applications.
The ferroelectricity emerging in non-polar graphene/hexagonal boron nitride (hBN) heterostructures has drawn considerable attention because of its fascinating properties and promising high-frequency electrical polarization switching. Yet, the underlying mechanism is still under debate. Here in twisted double bilayer graphene (TDBLG) aligned with its neighboring hBN, we observed two types of hysteresis-delayed hysteresis in top gate induced by the anomalous screening, and advanced hysteresis in back gate caused by the anomalous gate-tunable capacitance. To investigate the role played by moiré potential in the anomalous hysteresis, we studied a moiréless graphene heterostructure. Unexpectedly, we observed exactly the same phenomena in this control device. Our findings suggest that the anomalous ferroelectricity in graphene/hBN heterostructures may originate from the dielectric material hBN, calling for further structural investigations on hBN. Further analysis indicates that those hysteresis can be asymmetric and scalable with applied external electric fields, distinct from conventional ferroelectric switching with well-defined coercive fields. The observation of gate-tunable capacitance provides more insights in the mysterious ferroelectricity in graphene/hBN heterostructures, and should enable new design of memory devices such as memcapacitor based on tunable capacitance.
Visualizing the growth of two-dimensional materials is crucial for clarifying growth mechanisms and enabling controllable synthesis. Recent in situ electron microscopy has captured atomic-scale images of MoS2 growth, extending studies beyond post-growth characterization and theoretical simulations. Yet it remains unclear whether behavior observed under the demanding conditions of transmission electron microscopy and low vapor pressure applies to macroscopic vapor-phase synthesis. Here, we use in situ optical microscopy, Raman spectroscopy, electron microscopy, and device measurements to track the complete temperature-dependent conversion pathway of two-dimensional MoO2 nanosheets into MoS2 during sulfurization. The transformation is not a direct one-step phase transition. Rather, it follows a multistep pathway involving surface nucleation, formation of an amorphous Mo−S−O intermediate, local structural ordering, and final crystallization into layered MoS2. Partially sulfurized samples retain structural asymmetry, including an intermediate phase, voids, strain, and moiré fringes, while fully sulfurized samples form uniform layered crystals. Device measurements show that this structural evolution is accompanied by a transport transition from metallic MoO2 to semiconducting MoS2. Moreover, exfoliated MoS2 from partially sulfurized samples preserves local asymmetry and exhibits a pronounced pyroelectric effect under illumination, linking the conversion pathway with optoelectronic functionality.
Bismuth-based oxides are well known for their high Curie temperature and excellent fatigue resistance, which have attracted extensive researches and various applications. In this work, we successfully fabricated pure phase α-Bi2O3 films by a novel ultraviolet ozone oxidation method from β-Bi. The obtained α-Bi2O3 exhibits room-temperature out-of-plane ferroelectricity, as confirmed by both piezoelectric force microscopy measurements and hysteresis loops obtained from out-of-plane ferroelectric tunnel junctions. Density functional calculations predict that the ferroelectricity of α-Bi2O3 arises from a synergistic interplay between electric-field-induced structural deformation and charge redistribution within films. Our results demonstrate that such a thin room-temperature ferroelectric α-Bi2O3 film could be a promising candidate for future multifunctional electronic devices.
Bi2O2Se is a high-mobility, narrow-bandgap n-type layered semiconductor promising for broadband photodetection. However, its synthesis often relies on high temperatures or complex precursor systems that increase the thermal budget and limit device integration. Here we report a low-melting-point precursor-assisted chemical vapor deposition (CVD) strategy for growing high-quality Bi2O2Se nanosheets at 450 °C. Using elemental Bi and Se powders under an Ar/O2 atmosphere, we obtain single-crystalline nanosheets with uniform composition, long-term air stability and lateral sizes up to 0.6 mm. Photodetectors fabricated from the nanosheets show broadband response from 520 to 1550 nm, with a responsivity of 14.17 A∙W−1 and a specific detectivity of 6.39 × 1010 Jones at 1550 nm. The devices also exhibit fast response, with rise and fall times of 59 and 67 μs, respectively. Single-pixel imaging at 520 and 1550 nm further demonstrates their visible and near-infrared imaging capability. This work establishes low-melting-point precursor-assisted CVD as an effective route for low-temperature Bi2O2Se growth and points to its potential in broadband, high-speed photodetection.
CdZnTe films show great promise for applications in infrared imaging, solar cells, and radiation detection due to their excellent optoelectronic properties. However, single-crystal CdZnTe films directly deposited on commercial GaAs (001) substrate suffer from a high density of crystalline defects caused by a large lattice mismatch. Here we report the epitaxial growth of single-crystal CdZnTe films on GaAs (001) substrate using close spaced sublimation with a single-crystal ZnTe thin film as a buffer layer. As-grown CdZnTe films exhibit higher crystalline quality than those grown without a buffer layer. The optimal substrate temperature range is found to be 370−390 °C, and the growth rate reaches 94 μm/h. This work provides an approach to grow high-quality single-crystal CdZnTe films for optoelectronic device applications.
