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We fabricated a 1 × 10 PbS QD photodiode array with multiple stacked QD layers with high-resolution patterning using a customized photolithographic process. The array showed the average responsivity of 5.54 × 10−3 A/W and 1.20 × 10−2 A/W at 0 V and -1 V under 1310- nm short-wavelength infrared (SWIR) illumination. The standard deviation of the pixel responsivity was under 10%, confirming the uniformity of the fabrication process. The response time was 2.2 ± 0.13 ms, and the bandwidth was 159.1 Hz. A prototype 1310-nm SWIR imager demonstrated that the QD photodiode-based SWIR image sensor is a cost-effective and practical alternative for III-V SWIR image sensors.

Near-field mapping has been widely used to study hyperbolic phonon-polaritons in van der Waals crystals. However, an accurate measurement of the polaritonic loss remains challenging because of the inherent complexity of the near-field signal and the substrate-mediated loss. Here we demonstrate that large-area monocrystalline gold flakes, an atomically flat low-loss substrate for image polaritons, provide a platform for precise near-field measurement of the complex propagation constant of polaritons in van der Waals crystals. As a topical example, we measure propagation loss of the image phonon-polaritons in hexagonal boron nitride, revealing that their normalized propagation length exhibits a parabolic spectral dependency. Furthermore, we show that image phonon-polaritons exhibit up to a twice longer normalized propagation length, while being 2.4 times more compressed compared to the case of the dielectric substrate. We conclude that the monocrystalline gold flakes provide a unique nanophotonic platform for probing and exploitation of the image modes in low-dimensional materials.

Two-dimensional transition metal dichalcogenide semiconductors are very promising candidates for future electronic applications with low power consumption due to a low leakage current and high on-off current ratio. In this study, we suggest a complementary circuit consisting of ambipolar WSe2 and n-MoS2 field-effect transistors (FETs), which demonstrate dual functions of a frequency doubler and single inversion AND (SAND) logic gate. In order to reduce the power consumption, a high-quality thin h-BN single crystal is used as a gate dielectric that leads to a low operating voltage of less than 5 V. By combining the low operating voltage with a low operating current in the complementary circuit, a low power consumption of 300 nW (a minimum of 10 pW) has been achieved, which is a significant improvement compared to the tens of μW consumed by a graphene channel. The complementary circuit shows the effective frequency doubling of the input with a dynamic range from 20 to 100 Hz. Furthermore, this circuit satisfies all the truth tables of a SAND logic gate that can be used as a universal logic gate like NAND. Considering that the NAND logic gate generally consists of four transistors, it is significantly advantageous to implement the equivalent circuit SAND logic gate with only two FETs. Our results open up possibilities for analog- and logic-circuit applications based on low-dimensional semiconductors.

We report the effect of oxidation on PbS quantum dot (QD) photodetectors using rapid thermal annealing (RTA) and furnace annealing in air at different durations and temperatures. Air-annealed QD fi...

In this study, we demonstrated low leakage current and high mobility thin body (In)GaSb p-FETs. Through the optimization of the V/III ratio during the epitaxial growth, we achieved a highly insulating bottom Al0.95Ga0.05Sb barrier, which eliminates the junction leakage. We also suppressed the interface trap-assisted surface leakage current by introducing In0.53Ga0.47As surface passivation on the GaSb channel. Furthermore, GaSb/InGaSb/GaSb quantum well (QW) channel structure provided significant improvement in effective mobility ( ${\mu }_{\mathrm{ eff}}$ ) characteristics. As a result, the fabricated devices showed the lowest off-leakage current ( ${I} _{\mathrm{ off}}$ ), subthreshold slope ( ${S}$ . ${S}$ .) and high $\mu _{\mathrm{ eff}}$ among reported GaSb p-MOSFETs.

Two-dimensional transition-metal dichalcogenides (TMDs) have emerged as promising candidates for next-generation electronics owing to their excellent semiconducting properties. However, metal-TMDs junctions are of particular interest as they have become a major limiting factors to further improvements in TMD-based device performance. Here, we investigate the charge transport of MoS2 transistors contacted with Ti/Au and graphene electrodes. Compared to a conventional Ti/Au contact, the MoS2 devices with graphene electrodes exhibit improved electrical properties (field-effect mobility, subthreshold swing, and low off-state current). Such a device improvement could be attributed to efficient electron injection arising from the tunable graphene Fermi level as well as the high hole barrier height, which significantly reduces the off-state current caused by hole transport. Furthermore, a simple Schottky barrier model has been employed to explain the observed transfer characteristic of MoS2 transistors with two different contacts. Our finding provides significant insights into the understanding of charge transport in TMD-based transistors for future 2D electronics.

There is a growing demand for human-eye-invisible short-wave infrared (SWIR) detection due to its potential in applications in areas such as medical diagnostics, environmental monitoring, and night...

Precise control over the polarity of transistors is a key necessity for the construction of complementary metal-oxide-semiconductor circuits. However, the polarity control of 2D transistors remains a challenge because of the lack of a high-work-function electrode that completely eliminates Fermi-level pinning at metal-semiconductor interfaces. Here, a creation of clean van der Waals contacts is demonstrated, wherein a metallic 2D material, chlorine-doped SnSe

We report the performance of a MoS

A photoelectrochemical (PEC) cell produces hydrogen energy using solar energy and an electrochemical reaction. In the hydrogen production process with water decomposition, electrons move from the anode to the cathode, and by measuring the current value at this time, the PEC cell can generate hydrogen and function as an image sensor at the same time. Due to the characteristics of the PEC cell that can perform both functions simultaneously, it can be applied as a device that can detect and respond to the surrounding environment without the need for an observation system such as a camera. We present the imaging performance of PEC cells. The effectiveness of the experiment was confirmed by applying the PEC cells to integral imaging, one of the three-dimensional (3D) imaging techniques.

While 2D transition metal dichalcogenides (TMDs) are promising building blocks for various optoelectronic applications, limitations remain for multilayered TMD-based photodetectors: an indirect bandgap and a short carrier lifetime by strongly bound excitons. Accordingly, multilayered TMDs with a direct bandgap and an enhanced carrier lifetime are required for the development of various optoelectronic devices. Here, periodically arrayed nanopore structures (PANS) are proposed for improving the efficiency of multilayered p-WSe

Polarization-sensitive photodetection has attracted considerable attention as an emerging technology for future optoelectronic applications such as three-dimensional (3D) imaging, quantum optics, and encryption. However, traditional photodetectors based on Si or III-V InGaAs semiconductors cannot directly detect polarized light without additional optical components. Herein, we demonstrate a self-powered linear-polarization-sensitive near-infrared (NIR) photodetector using a two-dimensional WSe2/ReSe2 van der Waals heterostructure. The WSe2/ReSe2 heterojunction photodiode with semivertical geometry exhibits excellent performance: an ideality factor of 1.67, a broad spectral photoresponse of 405-980 nm with a significant photovoltaic effect, outstanding linearity with a linear dynamic range wider than 100 dB, and rapid photoswitching behavior with a cutoff frequency up to 100 kHz. Strongly polarized excitonic transitions around the band edge in ReSe2 lead to significant 980 nm NIR linear-polarization-dependent photocurrent. This linear polarization sensitivity remains stable even after exposure to air for longer than five months. Furthermore, by leveraging the NIR (980 nm)-selective linear polarization detection of this photodiode under photovoltaic operation, we demonstrate digital incoherent holographic 3D imaging. Accepted version

The probing of fundamental photophysics is a key prerequisite for the construction of diverse optoelectronic devices and circuits. To date, though, photocarrier dynamics in 2D materials remains unclear, plagued primarily by two issues: a large exciton binding energy, and the lack of a suitable system that enables the manipulation of excitons. Here, a WSe

Polarization-sensitive photodetection has attracted considerable attention as an emerging technology for future optoelectronic applications such as three-dimensional (3D) imaging, quantum optics, and encryption. However, traditional photodetectors based on Si or III-V InGaAs semiconductors cannot directly detect polarized light without additional optical components. Herein, we demonstrate a self-powered linear-polarization-sensitive near-infrared (NIR) photodetector using a two-dimensional WSe

Two-dimensional (2D) van der Waals (vdW) heterostructures herald new opportunities for conducting fundamental studies of new physical/chemical phenomena and developing diverse nanodevice applicatio...

Lead sulfide (PbS) quantum dots (QDs) have been researched for photovoltaic (PV) applications for decades. A large open-circuit voltage (Voc) deficit to bandgap is one of the drawbacks to overcome in PbS QD-based photovoltaics (QDPVs) compared to other photovoltaic systems. Here, we report the Voc improvement using a different Pb-precursor, PbCl2, which is known to have an better native ligand for chemical stability and photoluminescence quantum yield. We synthesized appropriate size of PbS QDs for PV applications by the Cademartiri method with modification. The PbCl2 precursors used in the Cademartiri method supply chloride ions (Cl−) for the atomic passivation. The Cl− as a native atomic ligand is substituted to iodide ions (I−) through post-synthesis ligand exchange process, and the remaining Cl− as a PbClx shell layer still exists after ligand exchange and passivates the QD surface. The Voc using PbS QDs from the Cademartiri synthesis is 20% larger than that from the Hines synthesis.

Metal-oxide semiconductors are very promising alternatives to amorphous and polycrystalline Si semiconductors. In addition to thin-film metal-oxide semiconductors, nanostructured metal-oxide semiconductors have also attracted considerable attention due to their interesting physical properties for versatile potential applications. Here, we report on metal-oxide semiconducting (InZnO and HfInZnO) nanofiber mats prepared by electrospinning. Thermal gravimetric analyses (TGA) and X-ray diffraction (XRD) measurements were carried out so as to investigate the phase transition from as-spun metal precursor/polymer matrix composite nanofibers mats to metal-oxide nanofiber mats. We fabricated field effect transistor (FETs) based on InZnO and HfInZnO nanofiber mats, and both FETs showed proper n-type transfer and output characteristics. FETs based on InZnO nanofiber mats-based FETs exhibited superior device performance: negligible hysteresis, a decent electron mobility of 5.49 cm2/Vs, and a good on/off current ratio of 107.

We herein demonstrate, for the first time, transparent, flexible, and large-area monolithic MoS2 transistors and logic gates. Each single transistor consists of only two components: a monolithic ch...

Precise control over the polarity of transistors is a key necessity for the construction of complementary metal–oxide–semiconductor circuits. However, the polarity control of two-dimensional (2D) transistors remains a challenge because of Fermi-level pinning resulting from disorders at metal–semiconductor interfaces. Here, we propose a strategy for clean van der Waals contacts, wherein a metallic 2D material, chlorine-doped SnSe2 (Cl–SnSe2), is used as the contact to provide an interface that is free of defects and Fermi-level pinning. Such clean contacts created via van der Waals integration of a 2D metal possess nearly ideal Schottky barrier heights, thus permitting polarity-controllable transistors. With the integration of 2D metallic Cl–SnSe2 as contacts, WSe2 transistors exhibit pronounced p-type characteristics, which are distinctly different from those of the devices with evaporated metal contacts, where n-type transport is observed. Finally, this ability to control the polarity enables the fabrication of functional logic gates and circuits, including inverter, NAND, and NOR.

Highly crystalline 2D/3D-mixed p-transition metal dichalcogenide (TMD)/n-Ga

A simple method for obtaining the charge carrier density of two-dimensional (2D) materials is proposed herein. A formula is suggested for the extraction of the 2D charge carrier density using the horizontal depletion width, which is visually represented by photocurrent mapping methods. An example of this method is demonstrated using a MoS2 Schottky diode. The results suggest that this method can be useful for a basic analysis of the physical properties of 2D devices.

Fiber optoelectronics technology has recently attracted attention as enabling various form factors of wearable electronics, and the issue of how to control and optimize the configuration and physical properties of the electrode micropatterns in the microfiber devices has become important. Here, spirally wrapped carbon nanotube (CNT) microelectrodes with a controlled dimension are demonstrated for high-performance fiber optoelectronic devices. Inkjet-printed CNT microelectrodes with the desired dimension on an agarose hydrogel template are rolling-transferred onto a microfiber surface with an efficient electrical interface. A fiber organic field-effect transistor with spirally wrapped CNT microelectrodes verifies the feasibility of this strategy, where the transferred microelectrodes intimately contact the organic semiconductor active layer and the output current characteristics are simply controlled, resulting in characteristics that exceed the previous structural limitations. Furthermore, a fiber organic photodiode with spirally wrapped CNT microelectrodes, when used as a transparent electrode, exhibits a high Ilight/Idark ratio and good durability of bending. This fiber photodiode can be successfully incorporated into a textile photoplethysmography bandage for the real-time monitoring of human vital signals. This work offers a promising and efficient strategy to overcome the geometric factors limiting the performance of fiber-optic optoelectronic devices.

In this study, flexible and transparent monolithic graphene transistors and complementary logic gates were fabricated using chemically doped graphene. The graphene channel was p- and n-doped with bis-(trifluoromethanesulfonyl)amine and poly(ethylene imine), respectively. Ion gel was utilized to gate the graphene transistor, and this facilitated low-voltage operation and yielded a coplanar-gate geometry. The resulting monolithic graphene transistors exhibited p-type or n-type transport depending on the type of dopant. The p-type and n-type graphene transistors were assembled together to fabricate various logic circuits, e.g., NOT, NAND, and NOR gates. Overall, the selective chemical doping of graphene enabled the realization of complementary logic gates, which represents a significant step in the application of graphene to future two-dimensional-based electronic devices.

Two-dimensional (2D) MoS2 is a representative n-type transition-metal dichalcogenide (TMD) semiconductor that has great potential for future nanoscale electronic and optoelectronic applications. He...

We report on InGaZnO (IGZO) thin film transistors (TFTs)-based bio-chemical sensors which can detect the chemical/biological species. As novel sensing platform, the IGZO TFT with Ag nanowire (NW) mesh showed pronounced output voltage changes responding to all analytes of H 2 O 2 , b- d -glucose, d -glucono-1,5-Lactione, and lactic acid, which are reproducible and reversible. Herein, porous Ag NW-functionalized top gate electrode plays a major role in sensing platform for enhanced sensing capability in aqueous medium. Moreover, these top gate geometry serve as a stable backplane for electrical modulation. As a result, analytes solutions become acidic or basic and such pH alterations induce significant turn-on voltage shifts on our devices. For implementation of a resistive load inverter, the output sensing voltage signals can be directly extracted, and such signals are reproducible and reversible. The proposed IGZO TFTs with Ag NW mesh top gate electrode based sensing platform pave the way for development of portable and reusable real-time non-destructive label-free chemical/biological sensors.

Surface engineering of the electron collecting layers (ECLs) is a straightforward and practical strategy to develop high performance inverted structure organic solar cells (OSCs). Here, we systematically investigate four different types of surface modified ECLs to implement high performance low-energy band gap poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-bA]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b ]-thiophenediyl] (PTB7) and [6,6]-phenyl-C70-butyric acid methyl ester (PC 70 BM) based inverted OSCs: (1) single PEIE, (2) ZnO:PEIE mixture (1:1 vol ratio), (3) PEIE/ZnO bilayer, and (4) ZnO/PEIE bilayer. OSCs with the ZnO/PEIE ECL show the highest power conversion efficiency (PCE) value of 8.61% while all the other devices exhibit PCE values of less than 7.80%. The excellent surface coverage as well as proper band alignment of the ZnO/PEIE bilayer leads to the highest device performance.

We report on the effects of zinc oxide (ZnO) morphology on the photovoltaic performance of inverted polymer solar cells (PSCs). Three different ZnO layers, fabricated from a sol–gel, nanoparticles (NPs), or nanorods (NRs), were employed as electron-collecting interlayers (ECIs) to compare their electrical, morphological, and optical properties in poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-bA]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7): [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM)-based inverted PSCs. The work functions of all the ZnO layers were lower than or similar to the electron affinity of the acceptor, PC70BM, allowing the ZnO-coated indium tin oxide (ITO) substrates to act as efficient electron-collecting electrodes. The ZnO NRs induced not only stronger scattering effects but also more efficient electron collection than those of the devices with ZnO sol‒gel or NP ECIs, resulting in enhanced external quantum efficiency and, consequently, the highest power conversion efficiency (8.38±0.09%) under illumination (AM 1.5G, 100 mW/cm2). The optical effects of the ZnO NRs were confirmed by a finite-difference time-domain simulation.

Touch screens have become an inherent part of the user interface in many electronics applications such as smartphones. The two types of developed touch sensors, the resistive and capacitive sensing devices, may face several difficulties when applied to flexible device applications such as touch signals arising from bending motions. In this study, we assess the feasibility of flexible touch sensors based on piezoelectric PbZr0.52Ti0.48O3 (PZT) thin films. Piezoelectric ceramic based flexible touch sensors possess unique advantages including scalable fabrication, fast response time, durability, and being self-powered. A demonstration device has been fabricated with a sandwich structure consisting of Pt electrode/functional PZT/Pt electrode/flexible substrate structure using laser lift-off (LLO) method. In order to anneal the functional PZT layer at high temperature (600 °C), the device was first fabricated on the sapphire substrate and transferred via melting sacrificial PZT layer with an excimer laser. We demonstrate the detection of x- and y-axis touch location via piezoelectric materials and confirm that the flexible piezoelectric touch sensors can distinguish between touch-induced and bending-induced signals via signal location, signal shape, and duration time. A notable feature of this fabrication technique involves its possibility to be fabricated in high resolution. This device may potentially achieve high resolution with suitable fabrication techniques, thus, providing the possibility for the next generation touch sensors.

The properties of vanadium-doped indium oxide (IVO) deposited at room temperature as a transparent conductor for inverted polymer solar cells have been investigated as a function of the vanadium doping concentration. IVO film prepared with V doping concentration of 0.03% showed optimal properties for use as a transparent conductor with figure of merit of 4.35 × 10−3 Ohm−1, related to altered band alignment between the Fermi level and conduction-band minimum. In the optimal optoelectrical conditions for the IVO film, performance optimization of PTB7:PC70BM inverted polymer solar cells resulted in maximum power conversion efficiency of 4.7 ± 0.4% under simulated air mass 1.5 global illumination at 100 mW/cm2.

Two-dimensional (2D) van der Waals (vdW) heterostructures herald new opportunities for conducting fundamental studies of new physical/chemical phenomena and developing diverse nanodevice applications. In particular, vdW heterojunction p-n diodes exhibit great potential as high-performance photodetectors, which play a key role in many optoelectronic applications. Here, we report on 2D MoTe

The properties of photoelectrochemical (PEC) cells have mainly been investigated with a focus on PEC hydrogen production. Because anodic current begins to flow when PEC cell is under illumination, and that this current varies as a function of light intensity, PEC cells can be used as a photodetector. Different from other image sensors, PEC cells can detect the light immersed in solutions due to their PEC properties. To verify the feasibility of using silicon-based PEC cell as an image sensor, we demonstrated a single pixel imaging system based on compressive sensing. Compressive sensing is an algorithm designed to recover signals from a small number of measurements, assuming that the signal of interest can be represented in a sparse way. In this study, we have demonstrated multispectral imaging using a siliconbased PEC cell with compressive sensing. The images were obtained in three primary colors (red, green, and blue). Due to the high photoresponse, stability and unique characteristic that silicon-based PEC cell can be used underwater, the silicon-based PEC cell is expected to be utilized in the future as a photodetector for various applications. We believe this study would be a great example of advanced developments in an optoelectronic system based on PEC cells.