An inorganic-blended p-type semiconductor with robust electrical and mechanical properties.

Inorganic semiconductors typically have limited p-type behavior due to the scarcity of holes and the localized valence band maximum, hindering the progress of complementary devices and circuits. In this work, we propose an inorganic blending strategy to activate the hole-transporting character in an inorganic semiconductor compound, namely tellurium-selenium-oxygen (TeSeO). By rationally combining intrinsic p-type semimetal, semiconductor, and wide-bandgap semiconductor into a single compound, the TeSeO system displays tunable bandgaps ranging from 0.7 to 2.2 eV. Wafer-scale ultrathin TeSeO films, which can be deposited at room temperature, display high hole field-effect mobility of 48.5 cm2/(Vs) and robust hole transport properties, facilitated by Te-Te (Se) portions and O-Te-O portions, respectively. The nanosphere lithography process is employed to create nanopatterned honeycomb TeSeO broadband photodetectors, demonstrating a high responsibility of 603 A/W, an ultrafast response of 5 µs, and superior mechanical flexibility. The p-type TeSeO system is highly adaptable, scalable, and reliable, which can address emerging technological needs that current semiconductor solutions may not fulfill.

Diffusion-Dominated Luminescence Dynamics of CsPbBr3 Studied Using Cathodoluminescence and Microphotoluminescence Spectroscopy.

Time-resolved or time-correlation measurements using cathodoluminescence (CL) reveal the electronic and optical properties of semiconductors, such as their carrier lifetimes, at the nanoscale. However, halide perovskites, which are promising optoelectronic materials, exhibit significantly different decay dynamics in their CL and photoluminescence (PL). We conducted time-correlation CL measurements of CsPbBr3 using Hanbury Brown-Twiss interferometry and compared them with time-resolved PL. The measured CL decay time was on the order of subnanoseconds and was faster than PL decay at an excited carrier density of 2.1 × 1018 cm-3. Our experiment and analytical model revealed the CL dynamics induced by individual electron incidences, which are characterized by highly localized carrier generation followed by a rapid decrease in carrier density due to diffusion. This carrier diffusion can play a dominant role in the CL decay time for undoped semiconductors, in general, when the diffusion dynamics are faster than the carrier recombination.

Pulse irradiation synthesis of metal chalcogenides on flexible substrates for enhanced photothermoelectric performance.

High synthesis temperatures and specific growth substrates are typically required to obtain crystalline or oriented inorganic functional thin films, posing a significant challenge for their utilization in large-scale, low-cost (opto-)electronic applications on conventional flexible substrates. Here, we explore a pulse irradiation synthesis (PIS) to prepare thermoelectric metal chalcogenide (e.g., Bi2Se3, SnSe2, and Bi2Te3) films on multiple polymeric substrates. The self-propagating combustion process enables PIS to achieve a synthesis temperature as low as 150 °C, with an ultrafast reaction completed within one second. Beyond the photothermoelectric (PTE) property, the thermal coupling between polymeric substrates and bismuth selenide films is also examined to enhance the PTE performance, resulting in a responsivity of 71.9 V/W and a response time of less than 50 ms at 1550 nm, surpassing most of its counterparts. This PIS platform offers a promising route for realizing flexible PTE or thermoelectric devices in an energy-, time-, and cost-efficient manner.

Multiscale Confinement Engineering for Boosting Overall Water Splitting by One-Step Stringing of a Single Atom and a Janus Nanoparticle within a Carbon Nanotube.

Enzyme-mimicking confined catalysis has attracted great interest in heterogeneous catalytic systems that can regulate the geometric or electronic structure of the active site and improve its performance. Herein, a liquid-assisted chemical vapor deposition (LCVD) strategy is proposed to simultaneously confine the single-atom Ru sites onto sidewalls and Janus Ni/NiO nanoparticles (NPs) at the apical nanocavities to thoroughly energize the N-doped carbon nanotube arrays (denoted as Ni/NiO@Ru-NC). The bifunctional Ni/NiO@Ru-NC electrocatalyst exhibits overpotentials of 88 and 261 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 100 mA cm-2 in alkaline solution, respectively, all ranking the top tier among the carbon-supported metal-based electrocatalysts. Moreover, once integrated into an anion-exchange membrane water electrolysis (AEMWE) system, Ni/NiO@Ru-NC can act as an efficient and robust bifunctional electrocatalyst to operate stably for 50 h under 500 mA cm-2. Theoretical calculations and experimental exploration demonstrate that the confinement of Ru single atoms and Janus Ni/NiO NPs can regulate the electron distribution with strong orbital couplings to activate the NC nanotube from sidewall to top, thus boosting overall water splitting.

Lattice-mismatch-free construction of III-V/chalcogenide core-shell heterostructure nanowires.

Growing high-quality core-shell heterostructure nanowires is still challenging due to the lattice mismatch issue at the radial interface. Herein, a versatile strategy is exploited for the lattice-mismatch-free construction of III-V/chalcogenide core-shell heterostructure nanowires by simply utilizing the surfactant and amorphous natures of chalcogenide semiconductors. Specifically, a variety of III-V/chalcogenide core-shell heterostructure nanowires are successfully constructed with controlled shell thicknesses, compositions, and smooth surfaces. Due to the conformal properties of obtained heterostructure nanowires, the wavelength-dependent bi-directional photoresponse and visible light-assisted infrared photodetection are realized in the type-I GaSb/GeS core-shell heterostructure nanowires. Also, the enhanced infrared photodetection is found in the type-II InGaAs/GeS core-shell heterostructure nanowires compared with the pristine InGaAs nanowires, in which both responsivity and detectivity are improved by more than 2 orders of magnitude. Evidently, this work paves the way for the lattice-mismatch-free construction of core-shell heterostructure nanowires by chemical vapor deposition for next-generation high-performance nanowire optoelectronics.

Controlling Surface Chemical Inhomogeneity of Ni2 P/MoNiP2 /MoP Heterostructure Electrocatalysts for Efficient Hydrogen Evolution Reaction.

Crystalline/amorphous phase engineering is demonstrated as a powerful strategy for electrochemical performance optimization. However, it is still a considerable challenge to prepare transition metal-based crystalline/amorphous heterostructures because of the low redox potential of transition metal ions. Herein, a facile H2 -assisted method is developed to prepare ternary Ni2 P/MoNiP2 /MoP crystalline/amorphous heterostructure nanowires on the conductive substrate. The characterization results show that the content of the MoNiP2 phase and the crystallinity of the MoP phase can be tuned by simply controlling the H2 concentration. The obtained electrocatalyst exhibits a superior alkaline hydrogen evolution reaction performance, delivering overpotentials of 20 and 76 mV to reach current densities of 10 and 100 mA cm-2 with a Tafel slope of 30.6 mV dec-1 , respectively. The catalysts also reveal excellent stability under a constant 100 h operation, higher than most previously reported electrocatalysts. These striking performances are ascribed to the optimized hydrogen binding energy and favorable hydrogen adsorption/desorption kinetics. This work not only exhibits the potential application of ternary Ni2 P/MoNiP2 /MoP crystalline/amorphous heterostructure nanowires catalysts for practical electrochemical water splitting, but also paves the way to prepare non-noble transition metal-based electrocatalysts with optimized crystalline/amorphous heterostructures.

Van der Waals nanomesh electronics on arbitrary surfaces.

Chemical bonds, including covalent and ionic bonds, endow semiconductors with stable electronic configurations but also impose constraints on their synthesis and lattice-mismatched heteroepitaxy. Here, the unique multi-scale van der Waals (vdWs) interactions are explored in one-dimensional tellurium (Te) systems to overcome these restrictions, enabled by the vdWs bonds between Te atomic chains and the spontaneous misfit relaxation at quasi-vdWs interfaces. Wafer-scale Te vdWs nanomeshes composed of self-welding Te nanowires are laterally vapor grown on arbitrary surfaces at a low temperature of 100 °C, bringing greater integration freedoms for enhanced device functionality and broad applicability. The prepared Te vdWs nanomeshes can be patterned at the microscale and exhibit high field-effect hole mobility of 145 cm2/Vs, ultrafast photoresponse below 3 µs in paper-based infrared photodetectors, as well as controllable electronic structure in mixed-dimensional heterojunctions. All these device metrics of Te vdWs nanomesh electronics are promising to meet emerging technological demands.

Contact Engineering of Halide Perovskites: Gold is Not Good Enough; Metalloid is Better.

The operation stability of halide perovskite devices is the critical issue that impedes their commercialization. The main reasons are that the ambient H2 O molecules can easily deteriorate the perovskites, while the metal electrodes react in different degrees with the perovskites. Herein, one kind of new electrode, the metalloids, is reported, which are much more stable than the conventional noble metals as electrical contacts for halide perovskites. The degradation mechanism of halide perovskites with noble metal electrodes is carefully studied and compared with the metalloid electrodes. It is found that the iodide ions can easily halogenate Cu and Ag in halide perovskites. Although Au is almost not halogenated, it can also decompose the perovskite film. On the contrary, after long-term storage, the metalloid electrodes remain intact on the perovskite film without any degradation. In addition, the long-time operation stability of the perovskite devices with metalloid electrodes is much higher than that of noble metals. First-principles calculations confirm the exceptional stability of the metalloid electrodes.This work explores the ultra-stable electrodes for halide perovskites, paving the way to the large-scale deployment of perovskite-based electronic devices.

Electrically Switchable Polarization in Bi2 O2 Se Ferroelectric Semiconductors.

Atomically 2D layered ferroelectric semiconductors, in which the polarization switching process occurs within the channel material itself, offer a new material platform that can drive electronic components toward structural simplification and high-density integration. Here, a room-temperature 2D layered ferroelectric semiconductor, bismuth oxychalcogenides (Bi2 O2 Se), is investigated with a thickness down to 7.3 nm (≈12 layers) and piezoelectric coefficient (d33 ) of 4.4 ± 0.1 pm V-1 . The random orientations and electrically dependent polarization of the dipoles in Bi2 O2 Se are separately uncovered owing to the structural symmetry-breaking at room temperature. Specifically, the interplay between ferroelectricity and semiconducting characteristics of Bi2 O2 Se is explored on device-level operation, revealing the hysteresis behavior and memory window (MW) formation. Leveraging the ferroelectric polarization originating from Bi2 O2 Se, the fabricated device exhibits "smart" photoresponse tunability and excellent electronic characteristics, e.g., a high on/off current ratio > 104 and a large MW to the sweeping range of 47% at VGS  = ±5 V. These results demonstrate the synergistic combination of ferroelectricity with semiconducting characteristics in Bi2 O2 Se, laying the foundation for integrating sensing, logic, and memory functions into a single material system that can overcome the bottlenecks in von Neumann architecture.

Au-Seeded CsPbI3 Nanowire Optoelectronics via Exothermic Nucleation.

Converting vapor precursors to solid nanostructures via a liquid noble-metal seed is a common vapor deposition principle. However, such a noble-metal-seeded process is excluded from the crystalline halide perovskite synthesis, mainly hindered by the growth mechanism shortness. Herein, powered by a spontaneous exothermic nucleation process (ΔH < 0), the Au-seeded CsPbI3 nanowires (NWs) growth is realized based on a vapor-liquid-solid (VLS) growth mode. It is energetically favored that the Au seeds are reacted with a Pb vapor precursor to form molten Au-Pb droplets at temperatures down to 212 °C, further triggering the low-temperature VLS growth of CsPbI3 NWs. More importantly, this Au-seeded process reduces in-bandgap trap states and consequently avoids Shockley-Read-Hall recombination, contributing to outstanding photodetector performances. Our work extends the powerful Au-seeded VLS growth mode to the emerging halide perovskites, which will facilitate their nanostructures with tailored material properties.

Mixed-Dimensional Anti-ambipolar Phototransistors Based on 1D GaAsSb/2D MoS2 Heterojunctions.

The incapability of modulating the photoresponse of assembled heterostructure devices has remained a challenge for the development of optoelectronics with multifunctionality. Here, a gate-tunable and anti-ambipolar phototransistor is reported based on 1D GaAsSb nanowire/2D MoS2 nanoflake mixed-dimensional van der Waals heterojunctions. The resulting heterojunction shows apparently asymmetric control over the anti-ambipolar transfer characteristics, possessing potential to implement electronic functions in logic circuits. Meanwhile, such an anti-ambipolar device allows the synchronous adjustment of band slope and depletion regions by gating in both components, thereby giving rise to the gate-tunability of the photoresponse. Coupled with the synergistic effect of the materials in different dimensionality, the hybrid heterojunction can be readily modulated by the external gate to achieve a high-performance photodetector exhibiting a large on/off current ratio of 4 × 104, fast response of 50 µs, and high detectivity of 1.64 × 1011 Jones. Due to the formation of type-II band alignment and strong interfacial coupling, a prominent photovoltaic response is explored in the heterojunction as well. Finally, a visible image sensor based on this hybrid device is demonstrated with good imaging capability, suggesting the promising application prospect in future optoelectronic systems.

High-performance electrically transduced hazardous gas sensors based on low-dimensional nanomaterials.

Low-dimensional nanomaterials have been proven as promising high-performance gas sensing components due to their fascinating structural, physical, chemical, and electronic characteristics. In particular, materials with low dimensionalities (i.e., 0D, 1D, and 2D) possess an extremely large surface area-to-volume ratio to expose abundant active sites for interactions with molecular analytes. Gas sensors based on these materials exhibit a sensitive response to subtle external perturbations on sensing channel materials via electrical transduction, demonstrating a fast response/recovery, specific selectivity, and remarkable stability. Herein, we comprehensively elaborate gas sensing performances in the field of sensitive detection of hazardous gases with diverse low-dimensional sensing materials and their hybrid combinations. We will first introduce the common configurations of gas sensing devices and underlying transduction principles. Then, the main performance parameters of gas sensing devices and subsequently the main underlying sensing mechanisms governing their detection operation process are outlined and described. Importantly, we also elaborate the compositional and structural characteristics of various low-dimensional sensing materials, exemplified by the corresponding sensing systems. Finally, our perspectives on the challenges and opportunities confronting the development and future applications of low-dimensional materials for high-performance gas sensing are also presented. The aim is to provide further insights into the material design of different nanostructures and to establish relevant design guidelines to facilitate the device performance enhancement of nanomaterial based gas sensors.

Gate Bias Stress Instability and Hysteresis Characteristics of InAs Nanowire Field-Effect Transistors.

Because of the excellent electrical properties, III-V semiconductor nanowires are promising building blocks for next-generation electronics; however, their rich surface states inevitably contribute large amounts of charge traps, leading to gate bias stress instability and hysteresis characteristics in nanowire field-effect transistors (FETs). Here, we investigated thoroughly the gate bias stress and hysteresis effects in InAs nanowire FETs. It is observed that the output current decreases together with the threshold voltage shifting to the positive direction when a positive gate bias stress is applied, and vice versa for the negative gate bias stress. For double-sweep transfer characteristics, the significant hysteresis behavior is observed, depending heavily on the sweeping rate and range. On the basis of complementary investigations of these devices, charge traps are confirmed to be the dominant factor for these instability effects. Importantly, the hysteresis can be simulated well by utilizing a combination of the rate equation for electron density and the empirical model for electron mobility. This provides an accurate evaluation of carrier mobility, which is in distinct contrast to the overestimation of mobility when using the transconductance for calculation. All these findings are important for understanding the charge trap dynamics to further enhance the device performance of nanowire FETs.

Artificial visual systems enabled by quasi-two-dimensional electron gases in oxide superlattice nanowires.

Rapid development of artificial intelligence techniques ignites the emerging demand on accurate perception and understanding of optical signals from external environments via brain-like visual systems. Here, enabled by quasi-two-dimensional electron gases (quasi-2DEGs) in InGaO3(ZnO)3 superlattice nanowires (NWs), an artificial visual system was built to mimic the human ones. This system is based on an unreported device concept combining coexistence of oxygen adsorption-desorption kinetics on NW surface and strong carrier quantum-confinement effects in superlattice core, to resemble the biological Ca2+ ion flux and neurotransmitter release dynamics. Given outstanding mobility and sensitivity of superlattice NWs, an ultralow energy consumption down to subfemtojoule per synaptic event is realized in quasi-2DEG synapses, which rivals that of biological synapses and now available synapse-inspired electronics. A flexible quasi-2DEG artificial visual system is demonstrated to simultaneously perform high-performance light detection, brain-like information processing, nonvolatile charge retention, in situ multibit-level memory, orientation selectivity, and image memorizing.

Perovskite Core-Shell Nanowire Transistors: Interfacial Transfer Doping and Surface Passivation.

While halide perovskite electronics are rapidly developing, they are greatly limited by the inferior charge transport and poor stability. In this work, effective surface charge transfer doping of vapor-liquid-solid (VLS)-grown single-crystalline cesium lead bromide perovskite (CsPbBr3) nanowires (NWs) via molybdenum trioxide (MoO3) surface functionalization is achieved. Once fabricated into NW devices, due to the efficient interfacial charge transfer and reduced impurity scattering, a 15× increase in the field-effect hole mobility (µh) from 1.5 to 23.3 cm2/(V s) is accomplished after depositing the 10 nm thick MoO3 shell. This enhanced mobility is already better than any mobility value reported for perovskite field-effect transistors (FETs) to date. The photodetection performance of these CsPbBr3/MoO3 core-shell NWs is also investigated to yield a superior responsivity (R) up to 2.36 × 103 A/W and an external quantum efficiency (EQE) of over 5.48 × 105% toward the 532 nm regime. Importantly, the MoO3 shell can provide excellent surface passivation to the CsPbBr3 NW core that minimizes the diffusion of detrimental water and oxygen molecules, improving the air stability of CsPbBr3/MoO3 core-shell NW devices. All these findings evidently demonstrate the surface doping as an enabling technology to realize high-mobility and air-stable low-dimensional halide perovskite devices.

Bication-Mediated Quasi-2D Halide Perovskites for High-Performance Flexible Photodetectors: From Ruddlesden-Popper Type to Dion-Jacobson Type.

Quasi-2D halide perovskites, especially the Ruddlesden-Popper perovskites (RPPs), have attracted great attention because of their promising properties for optoelectronics; however, there are still serious drawbacks, such as inefficient charge transport, poor stability, and unsatisfactory mechanical flexibility, restricting further utilization in advanced technologies. Herein, high-quality quasi-2D halide perovskite thin films are successfully synthesized with the introduction of the unique bication ethylenediammonium (EDA) via a one-step spin-coating method. This bication EDA, with short alkyl chain length, can not only substitute the typically bulky and weakly van der Waals-interacted organic bilayer spacer cations forming the novel Dion-Jacobson phase to enhance the mechanical flexibility of the quasi-2D perovskite (e.g., EDA(MA)n-1PbnI3n+1; MA = CH3NH3+) but also serve as a normal cation to achieve the more intact films (e.g., (iBA)2(MA)3-2x(EDA)xPb4I13). When fabricated into photodetectors, these optimized EDA-based perovskites deliver an excellent responsivity of 125 mA/W and a fast response time down to 380 µs under 532 nm irradiation. More importantly, the device with the Dion-Jacobson phase perovskite can be bent down to a radius of 2 mm and processed with 10,000 cycles of the bending test without any noticeable performance degradation because of its superior structure to RPPs. Besides, these films do not exhibit any material deterioration after ambient storage for 30 days. All these performance parameters are already comparable or even better than those of the state-of-the-art RPPs recently reported. This work provides valuable design guidelines of the quasi-2D perovskites to obtain high-performance flexible photodetectors for next-generation optoelectronics.

High-mobility In and Ga co-doped ZnO nanowires for high-performance transistors and ultraviolet photodetectors.

Due to their unique properties, ZnO nanostructures have received considerable attention for application in electronics and optoelectronics; however, intrinsic ZnO nanomaterials usually suffer from large concentrations of lattice defects, such as oxygen vacancies, which restricts their material performance. Here, for the first time, highly-crystalline In and Ga co-doped ZnO nanowires (NWs) are achieved by ambient-pressure chemical vapor deposition. In contrast to conventional elemental doping, this In and Ga co-doping can not only enhance the carrier concentration, but also suppresses the formation of oxygen vacancies within the host lattice of ZnO NWs. Importantly, this co-doping is also believed to effectively minimize the generation of lattice strain defects due to the optimal ionic sizes of both In and Ga dopants. When configured into field-effect transistors (FETs), these co-doped NWs exhibit an enhanced average electron mobility of 315 cm2 V-1 s-1 and an impressive on/off current ratio of 1.87 × 108, which are already higher than those of other previously reported ZnO NW devices. In addition, these NW devices demonstrate efficient ultraviolet photodetection at under 261 nm irradiation with an improved responsivity of 1.41 × 107 A W-1, an excellent EQE of up to 6.72 × 109 and a fast response time down to 0.32 s. Highly-ordered NW parallel array thin-film transistors and photodetectors are also constructed to demonstrate the promising potential of the NWs for high-performance device applications.

High-Performance Transparent Ultraviolet Photodetectors Based on InGaZnO Superlattice Nanowire Arrays.

Due to the efficient photocarrier separation and collection coming from their distinctive band structures, superlattice nanowires (NWs) have great potential as active materials for high-performance optoelectronic devices. In this work, InGaZnO NWs with superlattice structure and controllable stoichiometry are obtained by ambient-pressure chemical vapor deposition. Along the NW axial direction, perfect alternately stacking of InGaO(ZnO)4+ blocks and InO2- layers is observed to form a periodic layered structure. Strikingly, when configured into individual NW photodetectors, the Ga concentration is found to significantly influence the amount of oxygen vacancies and oxygen molecules adsorbed on the NW surface, which dictate the photoconducting properties of the NW channels. Based on the optimized Ga concentration (i.e., In1.8Ga1.8Zn2.4O7), the individual NW device exhibits an excellent responsivity of 1.95 × 105 A/W and external quantum efficiency of as high as 9.28 × 107% together with a rise time of 0.93 s and a decay time of 0.2 s for the ultraviolet (UV) photodetection. Besides, the obtained NWs can be fabricated into large-scale parallel arrays on glass substrates as well to achieve fully transparent UV photodetectors, where the performance is on the same level or even better than many transparent photodetectors with high performance. All the results discussed above demonstrate the great potential of InGaZnO superlattice NWs for next-generation advanced optoelectronic devices.

Utilizing a NaOH Promoter to Achieve Large Single-Domain Monolayer WS2 Films via Modified Chemical Vapor Deposition.

Because of their fascinating properties, two-dimensional (2D) nanomaterials have attracted a lot of attention for developing next-generation electronics and optoelectronics. However, there is still a lack of cost-effective, highly reproducible, and controllable synthesis methods for developing high-quality semiconducting 2D monolayers with a sufficiently large single-domain size. Here, utilizing a NaOH promoter and W foils as the W source, we have successfully achieved the fabrication of ultralarge single-domain monolayer WS2 films via a modified chemical vapor deposition method. With the proper introduction of a NaOH promoter, the single-domain size of monolayer WS2 can be increased to 550 µm, while the WS2 flakes can be well controlled by simply varying the growth duration and oxygen concentration in the carrier gas. Importantly, when they are fabricated into global backgated transistors, WS2 devices exhibit respectable peak electron mobility up to 1.21 cm2 V-1 s-1, which is comparable to those of many state-of-the-art WS2 transistors. Photodetectors based on these single-domain WS2 monolayers give an impressive photodetection performance with a maximum responsivity of 3.2 mA W-1. All these findings do not only provide a cost-effective platform for the synthesis of high-quality large single-domain 2D nanomaterials, but also facilitate their excellent intrinsic material properties for the next-generation electronic and optoelectronic devices.

Direct Vapor-Liquid-Solid Synthesis of All-Inorganic Perovskite Nanowires for High-Performance Electronics and Optoelectronics.

Controlled synthesis of lead halide perovskite (LHP) nanostructures not only benefits fundamental research but also offers promise for applications. Among many synthesis techniques, although catalytic vapor-liquid-solid (VLS) growth is recognized as an effective route to achieve high-quality nanostructures, until now, there is no detailed report on VLS grown LHP nanomaterials due to the emerging challenges in perovskite synthesis. Here, we develop a direct VLS growth for single-crystalline all-inorganic lead halide perovskite ( i.e., CsPbX3; X = Cl, Br, or I) nanowires (NWs). These NWs exhibit high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors (FET) based on individual CsPbX3 NWs are also fabricated, where they show the superior hole mobility of up to 3.05 cm2/(V s), higher than other all-inorganic LHP devices. This work provides important guidelines for the further improvement of these perovskite nanostructures for utilizations.