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Low temperature poly-crystalline silicon thin-film transistors (LTPS-TFTs) and indium-gallium-zinc-oxide TFTs (IGZO-TFTs) are potential candidates for future technology of various displays. Due to its simple manufacturing process, low cost and good uniformity, IGZO-TFTs have been developed as main stream display technology. From the viewpoint of device electrical characteristics, a-IGZO TFTs have better field-effect mobility (>10 cm2/V * s), larger Ion/Ioff ratio (>106), smaller subthreshold swing (S.S) and good stability. In this study, atmospheric-pressure PECVD (AP-PECVD) is used to deposit a-IGZO active layer, during the deposition process In-Situ hydrogenation is applied to enhance the layer characteristics. Also, the layer is then surface oxidation treated by neutral beam system (NBS). The optimal TFTs device characteristics is reached with In-Situ hydrogenation of H2 90 sccm, and surface oxidation of 400 W NBS treatment. The field-effect mobility is 34.05 cm2/V * s, threshold voltage is 1.74 V, subthreshold swing is 62 mV/decade, and current ratio Ion/Ioff is 2.04×107. Compared with conventional plasma, NBS used in this study provides charge-free plasma which could enhance device electric characteristics.

With better field-effect mobility (>10 cm2/V·S), smaller subthreshold swing (S.S), and other electrical characteristics, amorphous IGZO thin film transistors (a-IGZO TFTs) has been studied extensively for its promising applications, such as liquid crystal displays and flat-panel displays. In this investigation, TFT devices are experimented to enhance the electrical characteristics. Atmosphere Pressure-PECVD (AP-PECVD) is used to deposit a-IGZO, which is designed as device channel layer. In order to maintain enough gate control ability with thinner effective oxide thickness (EOT), high-κ material ZrO2 is used as dielectric, lowering the gate leaking current. With post dual neutral beams O2 plasma treated on both a-IGZO channel layer 400 W and ZrO2 dielectric 100 W, the best result for experimental devices show that the a-IGZO TFT has electrical characteristics of field-effect mobility of 22.22 cm2/V·S, threshold voltage (VT) of 2.86 V, S.S of 74 mV/decade, and Ion/Ioff ratio of 8.2×105. Keywor

Amorphous IGZO (a-IGZO) has been proved to be a suitable material for the channel layer in a thin film transistor, showing high mobility even in low temperature fabrication, device electrical characteristic exceeds a-Si or other metal oxide semiconductor materials. In this work, bottom gate top TFT is fabricated. With Atmosphere Pressure-PECVD (AP-PECVD), a-IGZO is deposited as device channel layer. A double channel layer is tested with Mg doping added in the bottom layer. This work focus on how the Mg doping concentration in the bottom layer affects device electrical characteristic. The result for best device characteristics is 5% Mg doping, showing highest mobility, lowest threshold voltage, and nearly 108 in Ion/Ioff. A suitable doping concentration can lower interface defect density and affect grain size, which both leads to a better device characteristics. However, device characteristics show sign of degradation with excess doping concentration.

Room-temperature optoelectronic devices that operate at short-wavelength and mid-wavelength infrared ranges (one to eight micrometres) can be used for numerous applications1-5. To achieve the range of operating wavelengths needed for a given application, a combination of materials with different bandgaps (for example, superlattices or heterostructures)6,7 or variations in the composition of semiconductor alloys during growth8,9 are used. However, these materials are complex to fabricate, and the operating range is fixed after fabrication. Although wide-range, active and reversible tunability of the operating wavelengths in optoelectronic devices after fabrication is a highly desirable feature, no such platform has been yet developed. Here we demonstrate high-performance room-temperature infrared optoelectronics with actively variable spectra by presenting black phosphorus as an ideal candidate. Enabled by the highly strain-sensitive nature of its bandgap, which varies from 0.22 to 0.53 electronvolts, we show a continuous and reversible tuning of the operating wavelengths in light-emitting diodes and photodetectors composed of black phosphorus. Furthermore, we leverage this platform to demonstrate multiplexed nondispersive infrared gas sensing, whereby multiple gases (for example, carbon dioxide, methane and water vapour) are detected using a single light source. With its active spectral tunability while also retaining high performance, our work bridges a technological gap, presenting a potential way of meeting different requirements for emission and detection spectra in optoelectronic applications.

Photostrictive materials that can reversibly change their structures in response to optical stimuli constitute an important class of functional smart materials and provide a mechanism for the micro-electromechanical systems. In this study, we show that monolayer WSe2 exhibits strong photostriction effect, a phenomenon where strain in materials can be induced by light irradiation. The photostriction in monolayer WSe2 can be as high as 2.5% under a light illumination of 7.7×106 mW cm-2, exhibiting the highest photostrictive coefficient among other semiconductor materials. Unlike the other non-polar materials, monolayer WSe2 shows gigantic light-induced strain at room temperature, and the deformation is reversible as the irradiation is turned off. We also observed that the photostrictive effect is pronounced in the monolayer but weak in the bilayer and few-layer WSe2. The pronounced gigantic photostriction in the monolayer is attributed to a combination of photovoltaic and inverse piezoelectric effects. This study opens up new applications of monolayer WSe2 for nano-opto-electro-mechanical platforms such as photo-actuators, nanogenerators, and photomicrosensors.

Monolayer transition metal dichalcogenides (TMDCs) are promising materials for next generation optoelectronic devices. The exciton diffusion length is a critical parameter that reflects the quality of exciton transport in monolayer TMDCs and limits the performance of many excitonic devices. Although diffusion lengths of a few hundred nanometers have been reported in the literature for as-exfoliated monolayers, these measurements are convoluted by neutral and charged excitons (trions) that coexist at room temperature due to natural background doping. Untangling the diffusion of neutral excitons and trions is paramount to understand the fundamental limits and potential of new optoelectronic device architectures made possible using TMDCs. In this work, we measure the diffusion lengths of neutral excitons and trions in monolayer MoS2 by tuning the background carrier concentration using a gate voltage and utilizing both steady state and transient spectroscopy. We observe diffusion lengths of 1.5 μm and 300 nm for neutral excitons and trions, respectively, at an optical power density of 0.6 W cm-2.

The range of luminescent materials that can be used in electroluminescent devices is limited due to material processing challenges and band alignment issues. This impedes the development of electroluminescent devices at extreme wavelengths and hinders the use of electroluminescence spectroscopy as an analytical technique. Here, we show that a two-terminal device that uses an array of carbon nanotubes as the source contact can excite electroluminescence from various materials independent of their chemical composition. Transient band bending, created by applying an a.c. gate voltage, is used to achieve charge injection across different band alignments. As a result, the device can produce electroluminescence from long-wave infrared (0.13 eV) to ultraviolet (3.3 eV) wavelengths depending on the emitting material drop-casted on top of the nanotube array, and with onset voltages approaching the optical energy gap of the emitting material. We show that our device can be used to probe a chemical reaction in a liquid droplet via electroluminescence spectroscopy and can be used as an electroluminescence sensor for detecting organic vapours. A two-terminal device that uses an array of carbon nanotubes as the source contact can excite electroluminescence from a variety of materials, producing electroluminescence from long-wave infrared to ultraviolet wavelengths, with onset voltages approaching the optical energy gap of the emitting material.

Copyright © 2020 American Chemical Society. Atomically thin semiconductors such as monolayer MoS2 and WS2 exhibit nonlinear exciton-exciton annihilation at notably low excitation densities (below ∼10 excitons/μm2 in exfoliated MoS2). Here, we show that the density threshold at which annihilation occurs can be tuned by changing the underlying substrate. When the supporting substrate is changed from SiO2 to Al2O3 or SrTiO3, the rate constant for second-order exciton-exciton annihilation, kXX [cm2/s], is reduced by 1 or 2 orders of magnitude, respectively. Using transient photoluminescence microscopy, we measure the effective room-temperature exciton diffusion coefficient in bis(trifluoromethane)sulfonimide-treated MoS2 to be in the range D = 0.03-0.06 cm2/s, corresponding to a diffusion length of LD = 350 nm for an exciton lifetime of τ = 18 ns, which does not depend strongly on the substrate. We discuss possible mechanisms for the observed behavior, including substrate permittivity, long-range exciton-exciton or exciton-charge interactions, defect-mediated Auger recombination, and spatially inhomogeneous exciton populations arising from substrate-induced disorder. Exciton annihilation limits the overall efficiency of 2D semiconductor devices operating at high exciton densities; the ability to tune these interactions via the underlying substrate is an important step toward more efficient optoelectronic technologies featuring atomically thin materials.

The mid-wave infrared (MWIR) wavelength range plays a central role in a variety of applications, including optical gas sensing, industrial process control, spectroscopy, and infrared (IR) countermeasures. Among the MWIR light sources, light-emitting diodes (LEDs) have the advantages of simple design, room-temperature operation, and low cost. Owing to the low Auger recombination at high carrier densities and direct bandgap of black phosphorus (bP), it can serve as a high quantum efficiency emitting layer in LEDs. In this work, we demonstrate bP-LEDs exhibiting high external quantum efficiencies and wall-plug efficiencies of up to 4.43 and 1.78%, respectively. This is achieved by integrating the device with an Al

There is an emerging need for semiconductors that can be processed at near ambient temperature with high mobility and device performance. Although multiple n-type options have been identified, the development of their p-type counterparts remains limited. Here, we report the realization of tellurium thin films through thermal evaporation at cryogenic temperatures for fabrication of high-performance wafer-scale p-type field-effect transistors. We achieve an effective hole mobility of ~35 cm2 V-1 s-1, on/off current ratio of ~104 and subthreshold swing of 108 mV dec-1 on an 8-nm-thick film. High-performance tellurium p-type field-effect transistors are fabricated on a wide range of substrates including glass and plastic, further demonstrating the broad applicability of this material. Significantly, three-dimensional circuits are demonstrated by integrating multi-layered transistors on a single chip using sequential lithography, deposition and lift-off processes. Finally, various functional logic gates and circuits are demonstrated.

High-photoluminescence quantum yield (PLQY) is required to reach optimal performance in solar cells, lasers, and light-emitting diodes (LEDs). Typically, PLQY can be increased by improving the material quality to reduce the nonradiative recombination rate. It is in principle equally effective to improve the optical design by nanostructuring a material to increase light out-coupling efficiency (OCE) and introduce quantum confinement, both of which can increase the radiative recombination rate. However, increased surface recombination typically minimizes nanostructure gains in PLQY. Here a template-guided vapor phase growth of CH3NH3PbI3 (MAPbI3) nanowire (NW) arrays with unprecedented control of NW diameter from the bulk (250 nm) to the quantum confined regime (5.7 nm) is demonstrated, while simultaneously providing a low surface recombination velocity of 18 cm s-1. This enables a 56-fold increase in the internal PLQY, from 0.81% to 45.1%, and a 2.3-fold increase in OCEy to increase the external PLQY by a factor of 130, from 0.33% up to 42.6%, exclusively using nanophotonic design.

Superacids are strong acids with an acidity higher than pure sulfuric acid. Recently, superacid treatment of monolayer transition metal dichalcogenide (TMDC) flakes, such as MoS2 and WS2, has shown a dramatic enhancement of optical properties, such as photoluminescence (PL) intensity. The superacid molecule is bis(trifluoromethane)sulfonimide (TFSI). In this review paper, we summarize and discuss the recent works and the current understanding of the TFSI treatment, and finally, we describe the outlook of the treatment on monolayer TMDCs.

Two-dimensional quantum dots have received a lot of attention in recent years due to their fascinating properties and widespread applications in sensors, batteries, white light-emitting diodes, photodetectors, phototransistors, etc. Atomically thin two-dimensional quantum dots derived from graphene, layered transition metal dichalcogenide, and phosphorene have sparked researchers’ interest with their unique optical and electronic properties, such as a tunable energy bandgap, efficient electronic transport, and semiconducting characteristics. In this review, we provide in-depth analysis of the characteristics of two-dimensional quantum dots materials, their synthesis methods, and opportunities and challenges for novel device applications. This analysis will serve as a tipping point for learning about the recent breakthroughs in two-dimensional quantum dots and motivate more scientists and engineers to grasp two-dimensional quantum dots materials by incorporating them into a variety of electrical and optical fields.

Semiconducting absorbers in high-performance short-wave infrared (SWIR) photodetectors and imaging sensor arrays are dominated by single-crystalline germanium and III-V semiconductors. However, these materials require complex growth and device fabrication procedures. Here, thermally evaporated Se

Significance A method is developed for enabling direct growth of shape-controlled single-crystal III–Vs on a wide range of substrates, including amorphous and/or low thermal budget substrates. Integration onto such substrates was previously limited by the high growth temperatures and lattice-match requirements of traditional deposition processes. Single-crystalline InP patterns are grown with substrate temperatures down to 220 °C by employing a templated liquid-phase crystallization method. InP grown by this method exhibits high electron mobilities and good optoelectronic properties, as demonstrated by the fabrication of high-performance transistors and light-emitting devices. The growth mode presents important practical implications for a broad spectrum of applications, as high-quality III–Vs can now be grown on virtually any substrate., III–V compound semiconductors are widely used for electronic and optoelectronic applications. However, interfacing III–Vs with other materials has been fundamentally limited by the high growth temperatures and lattice-match requirements of traditional deposition processes. Recently, we developed the templated liquid-phase (TLP) crystal growth method for enabling direct growth of shape-controlled single-crystal III-Vs on amorphous substrates. Although in theory, the lowest temperature for TLP growth is that of the melting point of the group III metal (e.g., 156.6 °C for indium), previous experiments required a minimum growth temperature of 500 °C, thus being incompatible with many application-specific substrates. Here, we demonstrate low-temperature TLP (LT-TLP) growth of single-crystalline InP patterns at substrate temperatures down to 220 °C by first activating the precursor, thus enabling the direct growth of InP even on low thermal budget substrates such as plastics and indium-tin-oxide (ITO)–coated glass. Importantly, the material exhibits high electron mobilities and good optoelectronic properties as demonstrated by the fabrication of high-performance transistors and light-emitting devices. Furthermore, this work may enable integration of III–Vs with silicon complementary metal-oxide-semiconductor (CMOS) processing for monolithic 3D integrated circuits and/or back-end electronics.

One of the long-standing problems in the field of organic electronics is their instability in an open environment, especially their poor water resistance. For the reliable operation of organic devices, introducing an effective protection layer using organo-compatible materials and processes is highly desirable. Here, we report a facile method for the depositing of an organo-compatible superhydrophobic protection layer on organic semiconductors under ambient conditions. The protection layer exhibiting excellent water-repellent and self-cleaning properties was deposited onto organic semiconductors directly using a dip-coating process in a highly fluorinated solution with fluoroalkylsilane-coated titanium dioxide (TiO2) nanoparticles. The proposed protection layer did not damage the underlying organic semiconductors and had good resistance against mechanical-, thermal-, light-stress-, and water-based threats. The protected organic field-effect transistors exhibited more-reliable electrical properties, even when exposed to strong solvents, due to its superhydrophobicity. This study provides a practical solution with which to enhance the reliability of environmentally sensitive organic semiconductor devices in the natural environment.

Developing multiple functionalities in nanodevices is a desirable objective in current nanotechnology, where the self-powered capability is one of the most demanded functions—without the need of external batteries, nanodevices can be operated independently and maintenance-free for a long period of time. In this study, we fabricated the core-shell nanostructured device employing multi-walled carbon nanotubes (CNTs) as inner cores and ZnO as outer shells, and demonstrate their multiple functionalities of fast UV detection and self-powered capability. The device features high photoconductive gain of 800 and short response time of 0.48 ms in air and 29 ms in vacuum. For energy harvesting, the device shows photovoltaic (PV) capability to drive a conventional liquid crystal display (LCD) with a Voc of 0.85 V and Isc of 5 nA. Those features demonstrate that our CNT-ZnO core-shell nanostructured device, performing both high photoresponsivity and PV capability, can be operated in different functionalities with or without external bias.

Flexible optoelectronics that can be bent, wrapped, and stretched have attracted interest for wearable and mobile applications. In this work, we demonstrate a transparent 360° omnidirectional photodetector (PD) that can be stretched and wrapped around flexible or curved substrates. By embedding interlaced ZnO and Ag nanowires (NWs) in thermoplastic polyurethane via inkjet printing, the device featured > 75% transmittance in the visible region, showing high photoresponsivity and response time (10–30 A/W and 0.8 s, respectively). Moreover, the flexible PD performs well under deformation (only 9% decay in the photocurrent under 60% strain and 8% loss when the device is bent at a radius of 5 mm), which allows it to be readily applied on curved surfaces, such as skin or optical fibers. This study opens the door for the development of flexible optoelectronics that could be implemented in fiber optics, wearable electronics, self-powered systems, bio-signal monitors, and epidermal electronics. Ink-jet printed nanowire network-polymer composites enable flexible, transparent photodetectorsthat can be bent, wrapped, and stretched.A collaborative team lead by Jr-Hau He from the Computer, Electrical and Mathematical Sciences and Engineering (CEMSE) Division at King Abdullah University of Science and Technology (KAUST) developed ink-jet printed 360° omnidirectional photodetectors that are fully transparent, stretchable and wrappable. The key to the device’s high degree of functionality is a polyurethane-based composite consisting of a ZnO-Ag interlaced nanowire network. Incorporating the composite into the device structure leads to photodetectors with over 75% transmittance, which enables omnidirectional photodetection with only 78% variation. The device operates under less than 5 mm bending radius and while stretched at over 60% strain, which allows the device to employed in applications such as wearable electronics.

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS2, WS2, MoSe2, and WSe2) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device., Atomically thin monolayers with high photoluminescence quantum yield are promising for optoelectronic and lighting applications. Here, the authors fabricate a transient-mode electroluminescent device to bypass the requirement of ohmic contacts for electrons and holes, and observe millimetre-scale light emission from a transparent 2D display.

Recently, there has been considerable research interest in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for future optoelectronic applications. It has been shown that surface passivation with the organic nonoxidizing superacid bis(trifluoromethane)sulfonamide (TFSI) produces MoS2 and WS2 monolayers whose recombination is at the radiative limit, with a photoluminescence (PL) quantum yield (QY) of ∼100%. While the surface passivation persists under ambient conditions, exposure to conditions such as water, solvents, and low pressure found in typical semiconductor processing degrades the PL QY. Here, an encapsulation/passivation approach is demonstrated that yields near-unity PL QY in MoS2 and WS2 monolayers which are highly stable against postprocessing. The approach consists of two simple steps: encapsulation of the monolayers with an amorphous fluoropolymer and a subsequent TFSI treatment. The TFSI molecules are able to diffuse through the encapsulation layer and passivate the defect state...

Excitons in two-dimensional (2D) materials are tightly bound and exhibit rich physics. So far, the optical excitations in 2D semiconductors are dominated by Wannier-Mott excitons, but molecular systems can host Frenkel excitons (FE) with unique properties. Here, we report a strong optical response in a class of monolayer molecular J-aggregates. The exciton exhibits giant oscillator strength and absorption (over 30% for monolayer) at resonance, as well as photoluminescence quantum yield in the range of 60–100%. We observe evidence of superradiance (including increased oscillator strength, bathochromic shift, reduced linewidth and lifetime) at room-temperature and more progressively towards low temperature. These unique properties only exist in monolayer owing to the large unscreened dipole interactions and suppression of charge-transfer processes. Finally, we demonstrate light-emitting devices with the monolayer J-aggregate. The intrinsic device speed could be beyond 30 GHz, which is promising for next-generation ultrafast on-chip optical communications., The optical response of inorganic two-dimensional semiconductors is dominated by Wannier-Mott excitons, but molecular systems can host localised Frenkel excitons. Here, the authors report strong optical response in a class of monolayer molecular J-aggregates due to the coherent Coulomb interaction between localised Frenkel excitons.

Author(s): Nguyen, V; Gramling, H; Towle, C; Li, W; Lien, DH; Kim, H; Chrzan, DC; Javey, A; Xu, K; Ager, J; Taylor, H | Abstract: One of the major challenges in the van der Waals (vdW) integration of two-dimensional (2D) materials is achieving high-yield and high-throughput assembly of predefined sequences of monolayers into heterostructure arrays. Mechanical exfoliation has recently been studied as a promising technique to transfer monolayers from a multilayer source synthesized by other techniques, allowing the deposition of a wide variety of 2D materials without exposing the target substrate to harsh synthesis conditions. Although a variety of processes have been developed to exfoliate the 2D materials mechanically from the source and place them deterministically onto a target substrate, they can typically transfer only either a wafer-scale blanket or one small flake at a time with uncontrolled size and shape. Here, we present a method to assemble arrays of lithographically defined monolayer WS2 and MoS2 features from multilayer sources and directly transfer them in a deterministic manner onto target substrates. This exfoliate-align-release process - without the need of an intermediate carrier substrate - is enabled by combining a patterned, gold-mediated exfoliation technique with a new optically transparent, heat-releasable adhesive. WS2/MoS2 vdW heterostructure arrays produced by this method show the expected interlayer exciton between the monolayers. Light-emitting devices using WS2 monolayers were also demonstrated, proving the functionality of the fabricated materials. Our work demonstrates a significant step toward developing mechanical exfoliation as a scalable dry transfer technique for the manufacturing of functional, atomically thin materials.

Electrostatic doping boosts emission Although monolayers of transition-metal dichalcogenides such as molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) should exhibit strong photoluminescence, in practice, defects in these materials can lead to very low quantum yields (less than 1%). Lien et al. show that as-formed MoS 2 and WS 2 monolayers encapsulated in poly(methyl methacrylate) can be electrostatically doped to achieve quantum yields near unity. Under these conditions, instead of charged trion species that recombine nonradiatively, only neutral excitons that recombine emissively form. These results help explain why coating these materials with certain Lewis acids also boosts the quantum yield. Science , this issue p. 468

There is an emerging need for semiconductors that can be processed at near ambient temperature with high mobility and device performance. Although multiple n-type options have been identified, the development of their p-type counterparts remains limited. Here, we report the realization of tellurium thin films through thermal evaporation at cryogenic temperatures for fabrication of high-performance wafer-scale p-type field-effect transistors. We achieve an effective hole mobility of ~35 cm

The reduction of carrier recombination processes by surface passivation is vital for highly efficient crystalline silicon (c-Si) solar cells and bulk wafer metrological characterization. Herein, we report a dip coating passivation of silicon surfaces in ambient air and temperature with Nafion, achieving a champion effective carrier lifetime of 12 ms on high resistivity n-type c-Si, which is comparable to state-of-the-art passivation methods. Nafion is a nonreactive polymer with strong Lewis acidity, thus leading to the formation of a large density of fixed charges at silicon surface, 1-2 orders of magnitude higher than what is achievable with conventional thin-film passivation layers. Notably, Nafion passivates the c-Si surface only by the fixed charges without chemical modification of dangling bonds, which is fundamentally different from the common practice of combining chemical with field-effect passivation. This dip coating process is simple and robust, without the need for complex equipment or parameter optimization as there is no chemical reaction involved.

A simple substrate decoupling method with optimized growth conditions enables a high-quality synthetic monolayer semiconductor., In recent years, there have been tremendous advancements in the growth of monolayer transition metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). However, obtaining high photoluminescence quantum yield (PL QY), which is the key figure of merit for optoelectronics, is still challenging in the grown monolayers. Specifically, the as-grown monolayers often exhibit lower PL QY than their mechanically exfoliated counterparts. In this work, we demonstrate synthetic tungsten diselenide (WSe2) monolayers with PL QY exceeding that of exfoliated crystals by over an order of magnitude. PL QY of ~60% is obtained in monolayer films grown by CVD, which is the highest reported value to date for WSe2 prepared by any technique. The high optoelectronic quality is enabled by the combination of optimizing growth conditions via tuning the halide promoter ratio, and introducing a simple substrate decoupling method via solvent evaporation, which also mechanically relaxes the grown films. The achievement of scalable WSe2 with high PL QY could potentially enable the emergence of technologically relevant devices at the atomically thin limit.

The thin-film vapor–liquid–solid (TF-VLS) growth technique presents a promising route for high quality, scalable, and cost-effective InP thin films for optoelectronic devices. Toward this goal, careful optimization of material properties and device performance is of utmost interest. Here, we show that exposure of polycrystalline Zn-doped TF-VLS InP to a hydrogen plasma (in the following referred to as hydrogenation) results in improved optoelectronic quality as well as lateral optoelectronic uniformity. A combination of low temperature photoluminescence and transient photocurrent spectroscopy was used to analyze the energy position and relative density of defect states before and after hydrogenation. Notably, hydrogenation reduces the relative intragap defect density by 1 order of magnitude. As a metric to monitor lateral optoelectronic uniformity of polycrystalline TF-VLS InP, photoluminescence and electron beam induced current mapping reveal homogenization of the grain versus grain boundary upon hydroge...

Optoelectronic devices based on two-dimensional (2D) materials have shown tremendous promise over the past few years; however, there are still numerous challenges that need to be overcome to enable their application in devices. These include improving their poor photoluminescence (PL) quantum yield (QY) as well as better understanding of exciton-based recombination kinetics. Recently, we developed a chemical treatment technique using an organic superacid, bis(trifluoromethane)sulfonimide (TFSI), which was shown to improve the quantum yield in MoS2 from less than 1% to over 95%. Here, we perform detailed steady-state and transient optical characterization on some of the most heavily studied direct bandgap 2D materials, specifically WS2, MoS2, WSe2, and MoSe2, over a large pump dynamic range to study the recombination mechanisms present in these materials. We then explore the effects of TFSI treatment on the PL QY and recombination kinetics for each case. Our results suggest that sulfur-based 2D materials are amenable to repair/passivation by TFSI, while the mechanism is thus far ineffective on selenium based systems. We also show that biexcitonic recombination is the dominant nonradiative pathway in these materials and that the kinetics for TFSI treated MoS2 and WS2 can be described using a simple two parameter model.

Semiconducting absorbers in high-performance short-wave infrared (SWIR) photodetectors and imaging sensor arrays are dominated by single-crystalline germanium and III-V semiconductors. However, these materials require complex growth and device fabrication procedures. Here, thermally evaporated Sex Te1- x alloy thin films with tunable bandgaps for the fabrication of high-performance SWIR photodetectors are reported. From absorption measurements, it is shown that the bandgaps of Sex Te1- x films can be tuned continuously from 0.31 eV (Te) to 1.87 eV (Se). Owing to their tunable bandgaps, the peak responsivity position and photoresponse edge of Sex Te1- x film-based photoconductors can be tuned in the SWIR regime. By using an optical cavity substrate consisting of Au/Al2 O3 to enhance its absorption near the bandgap edge, the Se0.32 Te0.68 film (an optical bandgap of ≈0.8 eV)-based photoconductor exhibits a cut-off wavelength at ≈1.7 μm and gives a responsivity of 1.5 AW-1 and implied detectivity of 6.5 × 1010 cm Hz1/2 W-1 at 1.55 μm at room temperature. Importantly, the nature of the thermal evaporation process enables the fabrication of Se0.32 Te0.68 -based 42 × 42 focal plane arrays with good pixel uniformity, demonstrating the potential of this unique material system used for infrared imaging sensor systems.

Two dimensional inorganic–organic hybrid perovskites (2D perovskites) suffer from not only quantum confinement, but also dielectric confinement, hindering their application perspective in devices involving the conversion of an optical input into current. In this report, we theoretically predict that an extremely low exciton binding energy can be achieved in 2D perovskites by using high dielectric-constant organic components. We demonstrate that in (HOCH2CH2NH3)2PbI4, whose organic material has a high dielectric constant of 37, the dielectric confinement is largely reduced, and the exciton binding energy is 20-times smaller than that in conventional 2D perovskites. As a result, the photo-induced excitons can be thermally dissociated efficiently at room temperature, as clearly indicated from femtosecond transient absorption measurements. In addition, the mobility is largely improved due to the strong screening effect on charge impurities. Such low dielectric-confined 2D perovskites show excellent carrier extraction efficiency, and outstanding humidity resistance compared to conventional 2D perovskites. Two-dimensional inorganic–organic hybrid perovskites are expected to play an important role in photovoltaic devices but suffer from issues related to dielectric confinement. The authors theoretically outline a method and experimentally succeed to overcome this issue by using materials with large dielectric constants.

One of the long-standing problems in the field of organic electronics is their instability in an open environment, especially their poor water resistance. For the reliable operation of organic devices, introducing an effective protection layer using organo-compatible materials and processes is highly desirable. Here, we report a facile method for the depositing of an organo-compatible superhydrophobic protection layer on organic semiconductors under ambient conditions. The protection layer exhibiting excellent water-repellent and self-cleaning properties was deposited onto organic semiconductors directly using a dip-coating process in a highly fluorinated solution with fluoroalkylsilane-coated titanium dioxide (TiO

We demonstrate bright electroluminescence in WSe 2 monolayers using pulsed injection, without the use of split gates, chemical doping, or heterostructures. Electroluminescence quantum efficiency approaches that of photoluminescence, indicating efficient exciton formation with injected carriers.

In the work, mechanisms behind various 3D nanocrystals enhanced performance of bulk heterojunction solar cells were studied comprehensively. Four types of gold nanoparticles (NPs) with distinctly different shapes and great uniformity were designed and synthesized, including cubes, rhombic dodecahedra (RD), edge- and corner-truncated octahedra (ECTO), and triangular plates, to systematically probe their influences on photovoltaics. RD and triangular plates show a higher growth rate, while slower growth favors cubes and ECTO formation by controlling the reduction agent and capping ion amount. NPs with increasing corners and proper size of cross-section induce stronger near-field coupling and far-field scattering in P3HT:PC61BM-based active layers. Both finite-difference time-domain simulation and UV–visible absorption spectra firmly support that RD exhibit the strongest localized surface plasmon resonance and optical scattering. With optimized conditions, a high power conversion efficiency exceeding 4% was ...

Two-dimensional layered semiconductors present a promising material platform for band-to-band-tunneling devices given their homogeneous band edge steepness due to their atomically flat thickness. Here, we experimentally demonstrate interlayer band-to-band tunneling in vertical MoS2/WSe2 van der Waals (vdW) heterostructures using a dual-gate device architecture. The electric potential and carrier concentration of MoS2 and WSe2 layers are independently controlled by the two symmetric gates. The same device can be gate modulated to behave as either an Esaki diode with negative differential resistance, a backward diode with large reverse bias tunneling current, or a forward rectifying diode with low reverse bias current. Notably, a high gate coupling efficiency of ∼80% is obtained for tuning the interlayer band alignments, arising from weak electrostatic screening by the atomically thin layers. This work presents an advance in the fundamental understanding of the interlayer coupling and electron tunneling in semiconductor vdW heterostructures with important implications toward the design of atomically thin tunnel transistors.