High-performance Optoelectronics Research Articles

Vertical Heterogeneous Integration of Metal Halide Perovskite Quantum-Wires/Nanowires for Flexible Narrowband Photodetectors

Charge collection narrowing (CCN) has been reported to be an efficient strategy to achieve optical filter-free narrowband photodetection (NPD) with metal halide perovskite (MHP) single crystals. However, the necessity of utilizing thick crystals in CCN limits their applications in large scale, flexible, self-driven, and high-performance optoelectronics. Here, for the first time, we fabricate vertically integrated MHP quantum wire/nanowire (QW/NW) array based photodetectors in nanoengineered porous alumina membranes (PAMs) showing self-driven broadband photodetection (BPD) and NPD capability simultaneously. Two cutoff detection edges of the NPDs are located at around 770 and 730 nm, with a full-width at half-maxima (fwhm) of around 40 nm. The optical bandgap difference between the NWs and the QWs, in conjunction with the high carrier recombination rate in QWs, contributes to the intriguing NPD performance. Thanks to the excellent mechanical flexibility of the PAMs, a flexible NPD is demonstrated with respectable performance. Our work here opens a new pathway to design and engineer a nanostructured MHP for novel color selective and full color sensing devices.

Schottky-Contacted High-Performance GaSb Nanowires Photodetectors Enabled by Lead-Free All-Inorganic Perovskites Decoration.

The surface Fermi level pinning effect promotes the formation of metal-independent Ohmic contacts for the high-speed GaSb nanowires (NWs) electronic devices, however, it limits next-generation optoelectronic devices. In this work, lead-free all-inorganic perovskites with broad bandgaps and low work functions are adopted to decorate the surfaces of GaSb NWs, demonstrating the success in the construction of Schottky-contacts by surface engineering. Benefiting from the expected Schottky barrier, the dark current is reduced to 2 pA, the Ilight /Idark ratio is improved to 103 and the response time is reduced by more than 15 times. Furthermore, a Schottky-contacted parallel array GaSb NWs photodetector is also fabricated by the contact printing technology, showing a higher photocurrent and a low dark current of 15 pA, along with the good infrared photodetection ability for a concealed target. All results guide the construction of Schottky-contacts by surface decorations for next-generation high-performance III-V NWs optoelectronics devices.

(INVITED)A diverse set of soliton molecules generation in a passively mode-locked Er-doped fiber laser with a saturable absorber of WSe2 nanofilm

WSe2, an intriguing transition metal dichalcogenides (TMDs) material with high-performance electronic and optoelectronics property, is emerging as next-generation photoelectronic devices. In this contribution, by applying WSe2 nanofilm as a saturable absorber in an Er-doped fiber laser, versatile mode-locked operations of conventional soliton, soliton molecules and dual-wavelength mode locked state can be experimentally observed. By properly setting the state of the polarization controller and pump power, the phase difference and pulse separation of soliton molecules can be adjusted. The soliton molecule with four steady phase difference (0, ±π/2, π) are realized in the fiber laser with TMDs based SA for the first time, to our knowledge. Meanwhile, a novel dual-wavelength mode-locked state with a soliton singlet and a soliton molecule is also obtained. Experiments results show that WSe2 is a suitable SA for vector soliton and soliton molecules generation.

Physics and applications of nanotubes

Nanotubes have been pursued aggressively over the last three decades. Significant progress has been made in the selective growth and post-synthetic sorting of highly monodisperse carbon nanotubes, in understanding their physics, and in assembling and integrating them into high-performance devices. These discoveries have led to promising applications in areas such as high-performance CMOS, high-speed RF, thin-film transistors, flexible electronics, thermoelectrics, sensors, and optoelectronics. The rapid development of modern information technology depends on the exploitation of new and novel materials, and nanotubes have emerged as promising candidates for the post-Moore's Law era. This Special Topic on Physics and Applications of Nanotubes provides a valuable forum where researchers studying the fundamentals of nanotubes can share their most recent and novel findings.

Photodetector based on liquid phase exfoliated SnSe quantum dots

Tremendous progress has been made in production of high-performance electronics and opto-electronics based on 2D-TMCs (Transition metal chalcogenides) due to their exotic band structure and unique physical properties. Herein, SnSe QDs, synthesized by liquid phase exfoliation, has an average size of 6 nm. Photodetector based on Ag/SnSe QDs/Ag shows non-ohmic charge transport with photoconducting behavior in visible to NIR spectral region. Photodetector shows quite distinct time resolved photoresponse with photoresponsivity of 401 μA/W in ambient environment and 36 μA/W in vacuum (10−3 torr) in illumination of 780 nm, 6 mW/cm2 light. Photoresponse with power law Iph α P0.7 shows that the photoresponse of detector is limited by defects in SnSe QDs. Photoswitching action is quite fast in vacuum than in ambient environment. Overall, the present findings demonstrate the influence of environmental oxygen on function of Ag/SnSe QDs/Ag photodetector.

Aligned CuO nanowire array for a high performance visible light photodetector

Recently, copper oxide (CuO) has drawn much attention as a promising material in visible light photodetection with its advantages in ease of nanofabrication. CuO allows a variety of nanostructures to be explored to enhance the optoelectrical performance such as photogenerated carriers scattering and bandgap engineering. However, previous researches neglect in-depth analysis of CuO’s light interaction effects, restrictively using random orientation such as randomly arranged nanowires, single nanowires, and dispersed nanoparticles. Here, we demonstrate an ultra-high performance CuO visible light photodetector utilizing perfectly-aligned nanowire array structures. CuO nanowires with 300 nm-width critical dimension suppressed carrier transport in the dark state and enhanced the conversion of photons to carriers; additionally, the aligned arrangement of the nanowires with designed geometry improved the light absorption by means of the constructive interference effect. The proposed nanostructures provide advantages in terms of dark current, photocurrent, and response time, showing unprecedentedly high (state-of-the-art) optoelectronic performance, including high values of sensitivity (S = 172.21%), photo-responsivity (R = 16.03 A/W, λ = 535 nm), photo-detectivity (D* = 7.78 × 1011 Jones), rise/decay time (τr/τd = 0.31 s/1.21 s).

Centimeter-Sized 2D Perovskitoid Single Crystals for Efficient X-ray Photoresponsivity

Metal-halide perovskitoids with corner-, edge-, and face-sharing octahedra provide a fertile “playground” for structure modulation. With low defect density, low ion migration, and high intrinsic stability, two-dimensional (2D) perovskitoid single crystals are expected to be ideal materials for room-temperature semiconductor detectors (RTSDs) as high-energy radiation. However, there is no report yet on the use of 2D perovskitoid single crystals for X-ray detection, as well as on how the halide-modulated molecular assembly would affect their structure and properties. Herein, based on an amidino-based organic spacer, we successfully synthesized a novel family of centimeter-sized 2D perovskitoid single crystals, (3AP)PbX4 (3AP = 3-amidinopyridine, X = Cl, Br, and I). This is the first time that centimeter-sized 2D perovskitoid single crystals are demonstrated for X-ray photoresponse. Detailed investigations reveal a unique crystal packing with corner-sharing and edge-sharing octahedra of inorganic frameworks and 3AP cations lying between adjacent inorganic layers in a parallel and antisymmetric manner. Changing the halide from I to Br and Cl results in greater Pb–X–Pb angles and stronger hydrogen bonding in perovskitoids and therefore consequently a better elastic recovery under stress, a more efficient charge transport in the inorganic layer, and a lower ionic migration. By varying halide substitution, an efficient X-ray photoresponse is achieved with a sensitivity up to 791.8 μC Gyair–1 cm–2 for (3AP)PbCl4 and a low detection limit of 1.54 μGyair s–1. These results reveal that the large 2D perovskitoid single crystals provide a promising platform for high performance optoelectronics.

Synthesis of interface modified MoS2/ZnO heterostructure via simple hydrothermal method and their enhanced UV photodetection characteristics with ultrafast photoresponse speed

Ultraviolet (UV) photodetectors employing ZnO nanorods (NRs) exhibit high photocurrent stability; however, UV photodetectors fabricated using ZnO NRs have several disadvantages. In this study, we fabricated high-performance UV photodetector using hydrothermally grown MoS2/ZnO heterostructure. The surface morphology of MoS2/ZnO heterostructure exhibited sea-urchin structure with a greater length and diameter than ZnO NRs. In addition, the formation of MoS2/ZnO heterostructure can form a type-II band alignment at interface between MoS2 and ZnO, which facilitates the regulation of electron movement with large surface area. With respect to UV photoresponse, MoS2/ZnO heterostructure exhibited a significantly improved photocurrent value compared to ZnO NRs and MoS2/ZnO heterostructure had extremely fast UV photoresponse speed with highly improved photoresponsivity, photosensitivity, and photoselectivity. Therefore, it was concluded that hydrothermally grown MoS2/ZnO heterostructure is a suitable solution to drawbacks of ZnO-based UV photodetectors; consequently, the proposed method can be used to fabricate ZnO-based high-performance optoelectronics applied in various fields.

High-Performance and Reliable White Organic Light-Emitting Fibers for Truly Wearable Textile Displays.

Light‐emitting fibers have been intensively developed for the realization of textile displays and various lighting applications, as promising free‐form electronics with outstanding interconnectivity. These advances in the fiber displays have been made possible by the successful implementation of the core technologies of conventional displays, including high optoelectronic performance and essential elements, in the fiber form‐factor. However, although white organic light‐emitting diodes (WOLEDs), as a fundamental core technology of displays, are essential for realizing full‐color displays and solid‐state lighting, fiber‐based WOLEDs are still challenging due to structural issues and the lack of approaches to implementing WOLEDs on fiber. Herein, the first fiber WOLED is reported, exhibiting high optoelectronic performance and a reliable color index, comparable to those of conventional planar WOLEDs. As key features, it is found that WOLEDs can be successfully introduced on a cylindrical fiber using a dip‐coatable single white‐emission layer based on simulation and optimization of the white spectra. Furthermore, to ensure durability from usage, the fiber WOLED is encapsulated by an Al2O3/elastomer bilayer, showing stable operation under repetitive bending and pressure, and in water. This pioneering work is believed to provide building blocks for realizing complete textile display technologies by complementing the lack of the core technology.

Stabilization of Metastable Halide Perovskite Lattices in the 2D Limit

Metal halide perovskites constitute a new class of semiconductors that are structurally tailorable, exhibiting rich structural polymorphs. In this perspective, the polymorphism in lead halide perovskites is described-a material system currently used for high-performance photovoltaics and optoelectronics. Strategies for stabilizing the metastable perovskite polymorphs based on crystal size reduction and surface functionalization are critically reviewed. Focus is on an unprecedented stabilization of metastable perovskite lattices in the 2D limit (e.g., with a thickness down to a few unit cells) due to the dominance of surface effects. This stabilization allows the incorporation of various A-cations that deemed oversized for 3D perovskites into the 2D perovskite lattices, which bring new insights on the relationships between the crystal structures and optoelectronic properties and lead to emergent ferroelectricity in halide perovskites. A comprehensive understanding is provided on how the A-cations influence the structural, optoelectronic, and ferroelectric properties, with an emphasis on the second order Jahn-Teller distortion caused by the oversized A-cations. Finally, future perspectives on new structure exploration and studies of fundamental photophysical properties using stabilized perovskite lattices are provided.

Biomimetic Hierarchically Silver Nanowire Interwoven MXene Mesh for Flexible Transparent Electrodes and Invisible Camouflage Electronics.

Flexible transparent electrodes demand high transparency, low sheet resistance, as well as excellent mechanical flexibility simultaneously, however they still remain to be a great challenge due to"trade-off" effect. Herein, inspired by a hollow interconnected leaf vein, we developed robust transparent conductive mesh with biomimetic interwoven structure via hierarchically self-assembles silver nanowires interwoven metal carbide/nitride (MXene) sheets along directional microfibers. Strong interfacial interactions between plant fibers and conductive units facilitate hierarchically interwoven conductive mesh constructed orderly on flexible and lightweight veins while maintaining high transparency, effectively avoiding the trade-off effect between optoelectronic properties. The flexible transparent electrodes exhibit sheet resistance of 0.5 Ω sq-1 and transparency of 81.6%, with a remarkably high figure of merit of 3523. In addition, invisible camouflage sensors are further successfully developed as a proof of concept that could monitor human body motion signals in an imperceptible state. The flexible transparent conductive mesh holds great potential in high-performance wearable optoelectronics and camouflage electronics.

Synthesis of GaSb-VDS thin film by electron beam physical vapour deposition and its electro-optical characterization as prerequisite for p-n device construction

III–V materials owing to have low effective masses, high mobilities and a direct band gap, exhibit suitability for both optoelectronic as well as tunnelling devices. Gallium Antimonide (GaSb), a III–V semiconducting compound, shows narrow band gap and high carrier mobility apposite for high-performance optoelectronics in the mid-IR range.The vertical directional solidification (VDS) is a crystal growth technique employed for the growth of high quality (>6N)bulk crystals, without the seed, without contact to the ampoule wall, without coating and without external pressure.Bulk crystalline GaSb was grown by VDS and then its fractured form is harnessed as source material for synthesis of thin film. GaSb-VDS thin semiconducting film of uniform thickness1.8μm was synthesized at 350°C by electron beam physical vapour deposition method.This thin film is p-type and will be implanted by group VI n-dopant(Telluriumions)impurities to form a junction. For same reason it is characterized for optical, electrical and morphological properties prior to support its claim as a device construction substrate. XRD, EDAX Raman, AFM, four probe and FTIR techniques were employed for the confirmation of crystalline, compositional, morphological, resistivity and optical band gap respectively.XRD of film reveals peaks close to 25°and42° corresponding to [111] and [220] crystal planes are in agreement as reported for crystalline GaSb. Raman spectra also confirm the GaSb crystalline film formation. SEM and EDAX of synthesized film found to be polycrystalline and agree the weight%of35.36and64.64 for GaandSb respectively. Four-probe technique yields the sheet resistance of 5.6Ωpersquare and optical band gap 0.728eV was obtained by FTIR. Optical band gap of the semiconducting film is obtained as 0.728eV and a Sheet resistance of5.6Ωpersquare. Uniform monolayer with low defect density is confirmed by Atomic force microscopy.It establishes formation of a p-type GaSb VDS thin film that is good for n-type implantation and show rectification tendency.

Fast and controllable synthesis of AB-stacked bilayer MoS2 for photoelectric detection

In recent years, researchers have explored the interlayer stacking structure of the bilayer (BL) transition metal dichalcogenides (TMDCs) and found that it has unique impact on the electrical, optical, and vibrational properties of TMDCs. Unfortunately, the size of BL TMDCs synthesized by the pre-existing methods is not large. In addition, there is not any effective mean to control the number of layers as well as the stack structure. This is the major limiting factor for further exploration of the properties of BL TMDCs. We report a new method for the rapid and controllable growth of AB-stacked BL MoS2. Firstly, the mixed solution of Na2MoO4 and NaOH was spun on the sapphire substrate and then sulfurated. The BL MoS2 of AB-stacked can be obtained by changing the time of sulfur introduction. The size of the BL MoS2 is related to the parameters of sulfur. The maximum size of BL MoS2 grown by this method can reach 288 μm, and the average size can reach about 200 μm, which is larger than the size reported in most articles. In addition, the growth rate of BL MoS2 can be clearly increased by the spin-coating growth method and the fastest growth rate is up to 144 μm min−1, which is far higher than other published reports at present. Subsequently, a photodetector based on BL MoS2 was prepared. The response time of rising edge is about 0.32 ms, and that of falling edge is about 3.2 ms. The detector prepared by us shows excellent photoelectric detection performance. Therefore, the excellent performance of BL MoS2 makes it have a broad application prospect in the field of high-performance electronics and optoelectronics.

Machine learning for high-throughput experimental exploration of metal halide perovskites

<h2>Summary</h2> Metal halide perovskites (MHPs) have catapulted to the forefront of energy research due to the unique combination of high device performance, low materials cost, and facile solution processability. A remarkable merit of these materials is their compositional flexibility allowing for multiple substitutions at all crystallographic sites, and hence thousands of possible pure compounds and virtually a near-infinite number of multicomponent solid solutions. Harnessing the full potential of MHPs necessitates rapid exploration of multidimensional chemical space toward desired functionalities. Recent advances in laboratory automation, ranging from bespoke fully automated robotic labs to microfluidic systems and to pipetting robots, have enabled high-throughput experimental workflows for synthesizing MHPs. Here, we provide an overview of the state of the art in the automated MHP synthesis and existing methods for navigating multicomponent compositional space. We highlight the limitations and pitfalls of the existing strategies and formulate the requirements for necessary machine learning tools including causal and Bayesian methods, as well as strategies based on co-navigation of theoritical and experimental spaces. We argue that ultimately the goal of automated experiments is to simultaneously optimize the materials synthesis and refine the theoretical models that underpin target functionalities. Furthermore, the near-term development of automated experimentation will not lead to the full exclusion of human operator but rather automatization of repetitive operations, deferring human role to high-level slow decisions. We also discuss the emerging opportunities leveraging machine learning-guided automated synthesis to the development of high-performance perovskite optoelectronics.

Substitutionally Doped MoSe2 for High-Performance Electronics and Optoelectronics.

2D materials, of which the carrier type and concentration are easily tuned, show tremendous superiority in electronic and optoelectronic applications. However, the achievements are still quite far away from practical applications. Much more effort should be made to further improve their performance. Here, p-type MoSe2 is successfully achieved via substitutional doping of Ta atoms, which is confirmed experimentally and theoretically, and outstanding homojunction photodetectors and inverters are fabricated. MoSe2 p-n homojunction device with a low reverse current (300 pA) exhibits a high rectification ratio (104 ). The analysis of dark current reveals the domination of the Shockley-Read-Hall (SRH) and band-to-band tunneling (BTB) current. The homojunction photodetector exhibits a large open-circuit voltage (0.68 V) and short-circuit currents (1 µA), which is suitable for micro-solar cells. Furthermore, it possesses outstanding responsivity (0.28 A W-1 ), large external quantum efficiency (42%), and a high signal-to-noise ratio (≈107 ). Benefiting from the continuous energy band of homojunction, the response speed reaches up to 20 µs. Besides, the Ta-doped MoSe2 inverter exhibits a high voltage gain (34) and low power consumption (127 nW). This work lays a foundation for the practical application of 2D material devices.

High Mobility Two-Dimensional Bismuth Oxyselenide Single Crystals with Large Grain Size Grown by Reverse-Flow Chemical Vapor Deposition.

2D semiconductors with atomically thin body thickness have attracted tremendous research interest for high-performance nanoelectronics and optoelectronics. Most of the 2D semiconductors grown by chemical vapor deposition (CVD) methods suffer from rather low carrier mobility, small single-crystal size, and instability under ambient conditions. Here, we develop an improved CVD method with controllable reverse-gas flow to realize the direct growth of quality Bi2O2Se 2D single crystals on a mica substrate. The applied reverse flow significantly suppresses the random nucleation and thus promotes the lateral size of 2D Bi2O2Se crystals up to ∼750 μm. The Bi2O2Se field-effect transistors display high-room-temperature electron mobility up to ∼1400 cm2·V-1·s-1 and a well-defined drain current saturation. The on/off ratio of the Bi2O2Se transistor is larger than 107, and the sub-threshold swing is about 90 mV·dec-1. The responsivity, response time, and detectivity of Bi2O2Se photodetectors approach up to 60 A·W-1, 5 ms, and 2.4 × 1010 Jones at room temperature, respectively. Our results demonstrate large-size and high-quality Bi2O2Se grown by reverse-flow CVD as a high-performance channel material for next-generation transistors and photodetectors.

Enhanced Emission from Interlayer Excitons Coupled to Plasmonic Gap Cavities.

The emergence of interlayer excitons (IEs) from atomic layered transition metal dichalcogenides (TMDCs) heterostructures has drawn tremendous attention due to their unique and exotic optoelectronic properties. Coupling the IEs into optical cavities provides distinctive electromagnetic environments which plays an important role in controlling multiple optical processes such as optical nonlinear generation or photoluminescence enhancement. Here, the integration of IEs in TMDCs into plasmonic nanocavities based on a nanocube on a metallic mirror is reported. Spectroscopic studies reveal an order of magnitude enhancement of the IE at room temperature and a 5-time enhancement in fluorescence at cryogenic temperatures. Cavity modeling reveals that the enhancement of the emission is attributed to both increased excitation efficiency and Purcell effect from the cavity. The results show a novel method to control the excitonic processes in TMDC heterostructures to build high performance photonics and optoelectronics devices.

Crystal Defect Investigation in PVT-Grown ZnSe Under Different Seeding Conditions and Growth Configurations Using Synchrotron X-Ray Topography

Zinc selenide (ZnSe) is a widely utilized II-VI semiconducting material for fabricating high-performance optoelectronics devices owing to its unique electrical and optical properties. As those properties highly depend on the native point defects and impurity distribution, achieving routine production of high-quality ZnSe crystal is essential. This study conducted synchrotron white beam X-ray topography (SWBXT), optical microscopy and high-resolution triple X-ray diffraction (HRTXD) characterization on five as-grown ZnSe boules grown in physical vapor transport (PVT) method with different seeding conditions and growth configurations. Study indicated that nucleation of multiple grains is induced during seeded growth, while self-seeded boules tend to obtain single crystals. ZnSe boules grown in vertical configuration are found to have relatively poor crystalline quality comparing to horizontally grown boules that are characterized by low energy facets. The twinning mechanism is also discussed. This study successfully investigated factors that induce crystal quality variation during the growth process.

Structural, electronic, and optic properties of Se nanotubes

A new category of tubular nanostructures solely composed of selenium was explored by using the density functional theory. Similar to those in carbon nanotubes, the armchair and zigzag tube-like structures formed as a roll-up α-Se nanoribbon. The zigzag (n ≤ 16, 0) nanotubes exhibit decreasingly narrow direct band gap, and the armchair (n, n) possess decreasingly moderate indirect gap. The strain energy of nanotubes is inversely proportional to the second power of the nanotube diameter. With increasing tube diameter, an initial rise and consequent decrease occurred in the effective masses to the limit value of α-Se monolayer. The carrier mobility of nanotubes is comparable with that of its monolayer with orders of 103 and 102 cm2V−1s−1 for electron and hole, respectively. The optical absorption spectra of α-Se nanotubes exhibit high absorbance in energy window cover the entire visible light spectrum. Therefore, α-Se nanotubes hold great potential for future applications in high-performance optoelectronics.

High hole mobility in physical vapour deposition-grown tellurium-based transistors.

Carrier mobility is one of most important figures of merit for materials that can determine to a large extent the corresponding device performances. So far, extensive efforts have been devoted to the mobility improvement of two-dimensional (2D) materials regarded as promising candidates to complement the conventional semiconductors. Graphene has amazing mobility but suffers from zero bandgap. Subsequently, 2D transition-metal dichalcogenides benefit from their sizable bandgap while the mobility is limited. Recently, the 2D elemental materials such as the representative black phosphorus can combine the high mobility with moderate bandgap; however the air-stability is a challenge. Here, we report air-stable tellurium flakes and wires using the facile and scalable physical vapour deposition (PVD) method. The prototype field-effect transistors were fabricated to exhibit high hole mobility up to 1485 cm2 V−1 s−1 at room temperature and 3500 cm2 V−1 s−1 at low temperature (2 K). This work can attract numerous attentions on this new emerging 2D tellurium and open up a new way for exploring high-performance optoelectronics based on the PVD-grown p-type tellurium.