Browsing by Author "Du, Mingde"

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Configurable anti-ambipolar photoresponses for optoelectronic multi-valued logic gates
(2024-07-29) Cui, Xiaoqi; Kim, Sunmean; Ahmed, Faisal; Du, Mingde; Liapis, Andreas C.; Muñoz, Juan Arias; Shafi, Abde Mayeen; Uddin, Md Gius; Ali, Fida; Zhang, Yi; Kang, Dong Ho; Lipsanen, Harri; Kang, Seokhyeong; Yoon, Hoon Hahn; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Anti-ambipolar transistors (AATs) are the leading platform for the paradigm shift from binary to multi-valued logic (MVL) circuits, increasing circuit integration density and data processing capacity. However, most AATs with p-n heterojunctions present limited controllability of the transconductance peak, which is key to MVL operation. Here, we report optically configurable AAT/bi-AAT photoresponses implemented with an InSe field-effect transistor for potential MVL operations. The charge trapping and detrapping processes incorporated with manually introduced trap states form the AAT peaks. Furthermore, leveraging a symmetric device configuration, the dark current is significantly suppressed, and AAT photoresponses are highlighted. Contributed by two pathways of trap states, the AAT/bi-AAT photoresponses are switchable by incident optical wavelength. This dependence facilitates optical wavelength to be one of the logic inputs for MVL, based on which we propose circuit-free ternary logic gates in a single device that can achieve more than ∼ 6 and ∼ 19 times improved data density (1 bit per transistor) for NMAX and XNOR, compared with such circuits in a traditional binary design. This work realizes optically controlled AAT photoresponses, paving the way to exploit optical wavelength as a new degree of freedom in MVL computing, offering a route toward ultra-high-density, ultra-low-power, and optically programmable optoelectronic integrated circuits.
Deterministic Light-to-Voltage Conversion with a Tunable Two-Dimensional Diode
(2022-08-17) Du, Mingde; Cui, Xiaoqi; Zhang, Bin; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Heterojunctions accompanied by energy barriers are of significant importance in two-dimensional materials-based electronics and optoelectronics. They provide more functional device performance, compared with their counterparts with uniform channels. Multimodal optoelectronic devices could be accomplished by elaborately designing band diagrams and architectures of the two-dimensional junctions. Here, we demonstrate deterministic light-to-voltage conversion based on strong dielectric screening effect in a tunable two-dimensional Schottky diode based on semiconductor/metal heterostructure, where the resultant photovoltage is dependent on the intensity of light input but independent of gate voltage. The converted photovoltage across the diode is independent of gate voltage under both monochromatic laser and white light illumination. In addition, the Fermi level of two-dimensional semiconductor area on dielectric SiO2 is highly gate-dependent, leading to the tunable rectifying effect of this heterostructure, which corporates a vertical Schottky junction and a lateral homojunction. As a result, a constant open-circuit voltage of ∼0.44 V and a hybrid “photovoltaic + photoconduction” photoresponse behavior are observed under 1 μW illumination of 403 nm laser, in addition to an electrical rectification ratio up to nearly 104. The scanning photocurrent mappings under different bias voltages indicate that the switchable operation mode (photovoltaic, photoconduction, or hybrid) depends on the bias-dependent effective energy barrier at the two-dimensional semiconductor–metal interface. This approach provides a facile and reliable solution for deterministic on-chip light-to-voltage conversion and optical-to-electrical interconnects.
Dual-gated mono-bilayer graphene junctions
(2021-01-21) Du, Mingde; Du, Luojun; Wei, Nan; Liu, Wei; Bai, Xueyin; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A lateral junction with an atomically sharp interface is extensively studied in fundamental research and plays a key role in the development of electronics, photonics and optoelectronics. Here, we demonstrate an electrically tunable lateral junction at atomically sharp interfaces between dual-gated mono- and bilayer graphene. The transport properties of the mono–bilayer graphene interface are systematically investigated with Ids–Vds curves and transfer curves, which are measured with bias voltage Vds applied in opposite directions across the asymmetric mono–bilayer interface. Nearly 30% difference between the output Ids–Vds curves of graphene channels measured at opposite Vds directions is observed. Furthermore, the measured transfer curves confirm that the conductance difference of graphene channels greatly depends on the doping level, which is determined by dual-gating. The Vds direction dependent conductance difference indicates the existence of a gate tunable junction in the mono–bilayer graphene channel, due to different band structures of monolayer graphene with zero bandgap and bilayer graphene with a bandgap opened by dual-gating. Simulation of the Ids–Vds curves based on a new numerical model validates the gate tunable junction at the mono–bilayer graphene interface from another point of view. The dual-gated mono–bilayer graphene junction and new protocol for Ids–Vds curve simulation pave a possible way for functional applications of graphene in next-generation electronics.
Flexible Micropillar Electrode Arrays for In Vivo Neural Activity Recordings
(2019-05-17) Du, Mingde; Guan, Shouliang; Gao, Lei; Lv, Suye; Yang, Siting; Shi, Jidong; Wang, Jinfen; Li, Hongbian; Fang, Ying
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Flexible electronics that can form tight interfaces with neural tissues hold great promise for improving the diagnosis and treatment of neurological disorders and advancing brain/machine interfaces. Here, the facile fabrication of a novel flexible micropillar electrode array (µPEA) is described based on a biotemplate method. The flexible and compliant µPEA can readily integrate with the soft surface of a rat cerebral cortex. Moreover, the recording sites of the µPEA consist of protruding micropillars with nanoscale surface roughness that ensure tight interfacing and efficient electrical coupling with the nervous system. As a result, the flexible µPEA allows for in vivo multichannel recordings of epileptiform activity with a high signal-to-noise ratio of 252 ± 35. The ease of preparation, high flexibility, and biocompatibility make the µPEA an attractive tool for in vivo spatiotemporal mapping of neural activity.
Highly Sensitive MoS2 Photodetectors Enabled with a Dry-Transferred Transparent Carbon Nanotube Electrode
(2023-01-25) Ding, Er-Xiong; Liu, Peng; Yoon, Hoon Hahn; Ahmed, Faisal; Du, Mingde; Shafi, Abde Mayeen; Mehmood, Naveed; Kauppinen, Esko I.; Sun, Zhipei; Lipsanen, Harri
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Fabricating electronic and optoelectronic devices by transferring pre-deposited metal electrodes has attracted considerable attention, owing to the improved device performance. However, the pre-deposited metal electrode typically involves complex fabrication procedures. Here, we introduce our facile electrode fabrication process which is free of lithography, lift-off, and reactive ion etching by directly press-transferring a single-walled carbon nanotube (SWCNT) film. We fabricated Schottky diodes for photodetector applications using dry-transferred SWCNT films as the transparent electrode to increase light absorption in photoactive MoS2 channels. The MoS2 flake vertically stacked with an SWCNT electrode can exhibit excellent photodetection performance with a responsivity of ∼2.01 × 103 A/W and a detectivity of ∼3.2 × 1012 Jones. Additionally, we carried out temperature-dependent current–voltage measurement and Fowler–Nordheim (FN) plot analysis to explore the dominant charge transport mechanism. The enhanced photodetection in the vertical configuration is found to be attributed to the FN tunneling and internal photoemission of charge carriers excited from indium tin oxide across the MoS2 layer. Our study provides a novel concept of using a photoactive MoS2 layer as a tunneling layer itself with a dry-transferred transparent SWCNT electrode for high-performance and energy-efficient optoelectronic devices.
Hybrid Photodetection Mechanisms Tuned with Tunneling
(2022) Yoon, Hoon Hahn; Fernandez, Henry A.; Nigmatulin, Fedor; Dai, Yunyun; Ahmed, Faisal; Cui, Xiaoqi; Bai, Xueyin; Li, Diao; Du, Mingde; Lipsanen, Harri; Sun, Zhipei
A4 Artikkeli konferenssijulkaisussa
In this paper, we report two strategies for realizing the hybrid photodetection mechanisms for high-performance broadband photodetectors built with tunable van der Waals (vdW) heterojunction interfaces. All electrically-controlled photoresponse tuned by the atomically-thin tunneling barrier and bandgap contrast across the vdW heterojunction interfaces can be used to adjust the tunneling resistance and suppress the dark current. Adjusting the hybrid photodetection through the switching operation can lead to an optimized optical switching ratio covering from the ultra-violet to the mid-infrared ranges. The representative device structures suitable for each strategy (1) naturally formed oxidation layer (2) energy band alignment, and their characterization exhibit how the hybrid gauge of the photodetection mechanisms can be tuned by quantum tunneling and charge trapping at the vdW heterointerfaces.
Magnetic actuation of flexible microelectrode arrays for neural activity recordings
(2019-10-03) Gao, Lei; Wang, Jinfen; Guan, Shouliang; Du, Mingde; Wu, Kun; Xu, Ke; Zou, Liang; Tian, Huihui; Fang, Ying
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Implantable microelectrodes that can be remotely actuated via external fields are promising tools to interface with biological systems at a high degree of precision. Here, we report the development of flexible magnetic microelectrodes (FMμEs) that can be remotely actuated by magnetic fields. The FMμEs consist of flexible microelectrodes integrated with dielectrically encapsulated FeNi (iron-nickel) alloy microactuators. Both magnetic torque- and force-driven actuation of the FMμEs have been demonstrated. Nano-platinum coated FMµEs have been applied for in vivo recordings of neural activities from peripheral nerves and cerebral cortex of mice. Moreover, owing to their ultra-small sizes and mechanical compliance with neural tissues, chronically implanted FMµEs elicited greatly reduced neuronal cell loss in mouse brain compared to conventional stiff probes. The FMµEs open up a variety of new opportunities for electrically interfacing with biological systems in a controlled and minimally-invasive manner.
Molybdenum Disulfide/Double-Wall Carbon Nanotube Mixed-Dimensional Heterostructures
(2022-05-04) Bai, Xueyin; Xu, Zhenyu; Zhang, Qiang; Li, Shisheng; Dai, Yunyun; Cui, Xiaoqi; Yoon, Hoon Hahn; Yao, Lide; Jiang, Hua; Du, Mingde; Zhang, Yi; Kauppinen, Esko I.; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Mixed-dimensional heterostructures which combine materials with different dimensions have emerged to expand the scope and functionality of van der Waals heterostructures. Here, a direct synthesis method of molybdenum disulfide/double-wall carbon nanotube (MoS2/DWCNT) mixed-dimensional heterostructures by sulfurating a molten salt, Na2MoO4, on a substrate covered with a DWCNT film is reported. The synthesized heterostructures are comprehensively characterized and their stacking order is confirmed to be MoS2 under the DWCNTs, although the DWCNT film is transferred on the substrate first. Moreover, field-effect transistors based on the heterostructure are fabricated for photodetection, and an abnormal negative photoresponse is discovered due to the strong carrier transfer in the mixed-dimensional heterostructures under light incidence. The MoS2/DWCNT heterostructure results provide a new approach for the synthesis and applications of mixed-dimensional heterostructures.
On-chip photonics and optoelectronics with a van der Waals material dielectric platform
(2022-07-07) Cui, Xiaoqi; Du, Mingde; Das, Susobhan; Yoon, Hoon Hahn; Pelgrin, Vincent Yves; Li, Diao; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
During the last few decades, photonic integrated circuits have increased dramatically, facilitating many high-performance applications, such as on-chip sensing, data processing, and inter-chip communications. The currently dominating material platforms (i.e., silicon, silicon nitride, lithium niobate, and indium phosphide), which have exhibited great application successes, however, suffer from their own disadvantages, such as the indirect bandgap of silicon for efficient light emission, and the compatibility challenges of indium phosphide with the silicon industry. Here, we report a new dielectric platform using nanostructured bulk van der Waals materials. On-chip light propagation, emission, and detection are demonstrated by taking advantage of different van der Waals materials. Low-loss passive waveguides with MoS2 and on-chip light sources and photodetectors with InSe have been realised. Our proof-of-concept demonstration of passive and active on-chip photonic components endorses van der Waals materials for offering a new dielectric platform with a large material-selection degree of freedom and unique properties toward close-to-atomic scale manufacture of on-chip photonic and optoelectronic devices.
Single-step chemical vapour deposition of anti-pyramid MoS2/WS2vertical heterostructures
(2021-02-28) Bai, Xueyin; Li, Shisheng; Das, Susobhan; Du, Luojun; Dai, Yunyun; Yao, Lide; Raju, Ramesh; Du, Mingde; Lipsanen, Harri; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Van der Waals heterostructures are the fundamental building blocks of electronic and optoelectronic devices. Here we report that, through a single-step chemical vapour deposition (CVD) process, high-quality vertical bilayer MoS2/WS2 heterostructures with a grain size up to ∼60 μm can be synthesized from molten salt precursors, Na2MoO4 and Na2WO4. Instead of normal pyramid vertical heterostructures grown by CVD, this method synthesizes an anti-pyramid MoS2/WS2 structure, which is characterized by Raman, photoluminescence and second harmonic generation microscopy. Our facile CVD strategy for synthesizing anti-pyramid structures unveils a new synthesis route for the products of two-dimensional heterostructures and their devices for application.
Switchable Photoresponse Mechanisms Implemented in Single van der Waals Semiconductor/Metal Heterostructure
(2022-01-25) Du, Mingde; Cui, Xiaoqi; Yoon, Hoon Hahn; Das, Susobhan; Uddin, Md; Du, Luojun; Li, Diao; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
van der Waals (vdW) heterostructures based on two-dimensional (2D) semiconducting materials have been extensively studied for functional applications, and most of the reported devices work with sole mechanism. The emerging metallic 2D materials provide us new options for building functional vdW heterostructures via rational band engineering design. Here, we investigate the vdW semiconductor/metal heterostructure built with 2D semiconducting InSe and metallic 1T-phase NbTe2, whose electron affinity χInSe and work function ΦNbTe2 almost exactly align. Electrical characterization verifies exceptional diode-like rectification ratio of >103 for the InSe/NbTe2 heterostructure device. Further photocurrent mappings reveal the switchable photoresponse mechanisms of this heterostructure or, in other words, the alternative roles that metallic NbTe2 plays. Specifically, this heterostructure device works in a photovoltaic manner under reverse bias, whereas it turns to phototransistor with InSe channel and NbTe2 electrode under high forward bias. The switchable photoresponse mechanisms originate from the band alignment at the interface, where the band bending could be readily adjusted by the bias voltage. In addition, a conceptual optoelectronic logic gate is proposed based on the exclusive working mechanisms. Finally, the photodetection performance of this heterostructure is represented by an ultrahigh responsivity of ∼84 A/W to 532 nm laser. Our results demonstrate the valuable application of 2D metals in functional devices, as well as the potential of implementing photovoltaic device and phototransistor with single vdW heterostructure.
Tunable Quantum Tunneling through a Graphene/Bi2Se3 Heterointerface for the Hybrid Photodetection Mechanism
(2021-12-15) Yoon, Hoon Hahn; Ahmed, Faisal; Dai, Yunyun; Fernandez Pizarro, Henry; Cui, Xiaoqi; Bai, Xueyin; Li, Diao; Du, Mingde; Lipsanen, Harri; Sun, Zhipei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Graphene-based van der Waals heterostructures are promising building blocks for broadband photodetection because of the gapless nature of graphene. However, their performance is mostly limited by the inevitable trade-off between low dark current and photocurrent generation. Here, we demonstrate a hybrid photodetection mode based on the photogating effect coupled with the photovoltaic effect via tunable quantum tunneling through the unique graphene/Bi2Se3 heterointerface. The tunneling junction formed between the semimetallic graphene and the topologically insulating Bi2Se3 exhibits asymmetric rectifying and hysteretic current-voltage characteristics, which significantly suppresses the dark current and enhances the photocurrent. The photocurrent-to-dark current ratio increases by about a factor of 10 with the electrical tuning of tunneling resistance for efficient light detection covering the major photonic spectral band from the visible to the mid-infrared ranges. Our findings provide a novel concept of using tunable quantum tunneling for highly sensitive broadband photodetection in mixed-dimensional van der Waals heterostructures.
Wafer-Scale Fabrication of Wearable All-Carbon Nanotube Photodetector Arrays
(2024-07-23) Liu, Peng; Ding, Er Xiong; Xu, Zhenyu; Cui, Xiaoqi; Du, Mingde; Zeng, Weijun; Karakassides, Anastasios; Zhang, Jin; Zhang, Qiang; Ahmed, Faisal; Jiang, Hua; Hakonen, Pertti; Lipsanen, Harri; Sun, Zhipei; Kauppinen, Esko I.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
With electronic devices evolving toward portable and high-performance wearables, the constraints of complex and wet processing technologies become apparent. This study presents a scalable photolithography/chemical-free method for crafting wearable all-carbon nanotube (CNT) photodetector device arrays. Laser-assisted patterning and dry deposition techniques directly assemble gas-phase CNTs into flexible devices without any lithography or lift-off processes. The resulting wafer-scale all-CNT photodetector arrays showcase excellent uniformity, wearability, environmental stability, and notable broadband photoresponse, boasting a high responsivity of 44 AW-1 and a simultaneous detectivity of 1.9 × 109 Jones. This research provides an efficient, versatile, and scalable strategy for manufacturing wearable all-CNT device arrays, allowing widespread adoption in wearable optoelectronics and multifunctional sensors.