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Hybrid organolead halide perovskites have attracted tremendous attention due to their recent success as high efficiency solar cell materials and their fascinating material properties uniquely suitable for optoelectronic devices. However, the poor ambient and operational stability as well as the concern of lead toxicity greatly hamper their practical utilization. In this work, crystalline, all-inorganic and lead-free Cs3Sb2I9 perovskite microplates are successfully synthesized by a two-step chemical vapor deposition method. As compared with other typical lead-free perovskite materials, the Cs3Sb2I9 microplates demonstrate excellent optoelectronic properties, including substantial enhancements in the Stokes shift, exciton binding energy and electron-phonon coupling. Simple photoconductive devices fabricated using these microplates exhibit an ultra-fast response with the rise and decay time constants down to 96 and 58 µs, respectively. This respectable photoconductor performance can be regarded as a record among all the lead-free perovskite materials. Importantly, these photodetectors show superior thermal stability in a wide temperature range, capable to function reversibly between 80 and 380 K, indicating their robustness to operate under both low and high temperatures. All these results evidently suggest the technological potential of inorganic lead-free Cs3Sb2I9 perovskite microplates for next-generation high-performance optoelectronic devices.

Due to the enhanced ambient structural stability and excellent optoelectronic properties, all-inorganic metal halide perovskite nanowires have become one of the most attractive candidates for flexible electronics, photovoltaics and optoelectronics. Their elastic property and mechanical robustness become the key factors for device applications under realistic service conditions with various mechanical loadings. Here, we demonstrate that high tensile elastic strain (∼ 4% to ∼ 5.1%) can be achieved in vapor-liquid-solid-grown single-crystalline CsPbBr3 nanowires through in situ scanning electron microscope (SEM) buckling experiments. Such high flexural elasticity can be attributed to the structural defect-scarce, smooth surface, single-crystallinity and nanomechanical size effect of CsPbBr3 nanowires. The mechanical reliability of CsPbBr3 nanowire-based flexible photodetectors was examined by cyclic bending tests, with no noticeable performance deterioration observed after 5,000 cycles. The above results suggest great application potential for using all-inorganic perovskite nanowires in flexible electronics and energy harvesting systems.

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.

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.

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.

Due to the excellent electrical and optical properties, small bandgap III–V nanowire (NW) materials hold great promise for future electronics and optoelectronics. In particular, InAs1−xSbx, the ternary alloy of InAs and InSb, is one of the most studied III–V nanomaterial systems; however, the As-rich InAs1−xSbx NWs are usually obtained with significant crystal phase mixing and high density of planar defects, limiting their electrical transport characteristics. In this work, unusual phase-pure zinc blende and highly-crystalline As-rich InAs1−xSbx NWs with x < 0.2 are successfully achieved using solid-source chemical vapor deposition, and this excellent phase-purity and crystallinity has not been reported elsewhere. By simply controlling the precursor powder mixing ratio between InAs and InSb, the morphology and composition of NWs can be controlled reliably. When these InAs1−xSbx NWs are fabricated into field-effect transistors, they exhibit a superior device performance, especially a high electron mobility. Specifically, the average peak mobility of the InAs0.948Sb0.052 NW device can be improved up to 3160 cm2 V−1 s−1, which is substantially better than that of the pure InAs NW counterparts (2030 cm2 V−1 s−1). This mobility enhancement can be attributed to the Sb-alloyed-induced electron effective mass reduction. Also, there exists a surface charge accumulation layer on the NWs as confirmed by the decrease of device transconductance measured under vacuum, indicating future possibilities to manipulate the NW surface for enhanced functionality. All these results evidently indicate the potential of these phase-pure zinc blende As-rich InAs1−xSbx NWs for high-mobility devices.

In this letter, high-performance thin-film transistors (TFTs), with indium oxide (In2O3) as front channel layer, high permittivity ZrO2 as dielectric layer, and aluminum oxide (Al2O3) as passivation layers were integrated by a fully solution process. It is found that the incorporation of Al2O3 passivation layer gives rise to a sharp decrease in the off current (Ioff) and a corresponding increase in the on/off current ratio ( $\text{I}_{\text {on}}$ /Ioff) of the TFTs, compared to that without Al2O3 passivation. Furthermore, the thickness effect of the passivation layer on the performance of In2O3 /ZrO2 TFTs has been investigated systematically. The In2O3 /ZrO2 TFTs with optimized Al2O3 passivation layers can be operated at 3 V with high performance, including a high field-effect mobility of 21.22 cm2 /V s, a large $\text{I}_{\text {on}}$ /I off of 107 and a negligible hysteresis (~0V). This work demonstrates an effective strategy for the construction of high performance TFTs by incorporating the passivation layer.

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)

Amorphous indium—gallium—zinc oxide (a-IGZO) materials have been widely explored for various thin-film transistor (TFT) applications; however, their device performance is still restricted by the intrinsic material issues especially due to their non-crystalline nature. In this study, highly crystalline superlattice-structured IGZO nanowires (NWs) with different Ga concentration are successfully fabricated by enhanced ambient-pressure chemical vapor deposition (CVD). The unique superlattice structure together with the optimal Ga concentration (i.e., 31 at.%) are found to effectively modulate the carrier concentration as well as efficiently suppress the oxygen vacancy formation for the superior NW device performance. In specific, the In1.8Ga1.8Zn24O7 NW field-effect transistor exhibit impressive device characteristics with the average electron mobility of ~ 110 cm2·V−1·s−1 and on/off current ratio of ~ 106. Importantly, these NWs can also be integrated into NW parallel arrays for the construction of high-performance TFT devices, in which their performance is comparable to many state-of-the-art IGZO TFTs. All these results can evidently indicate the promising potential of these crystalline superlattice-structured IGZO NWs for the practical utilization in next-generation metal-oxide TFT device technologies.

Group III oxides, such as In2O3 and Ga2O3, have proved to be good candidates as active materials for novel electronic devices, including high-mobility transistors, gas sensors, and UV photodetectors. The ability to tune optical and electronic properties is provided by alloying In2 xGa2-2 xO3 (InGaO) in a broad compositional range. Further development of InGaO compounds in the form of nanowires (NWs) would overcome the technological limitations, such as the substrate crystal lattice mismatch and the inability to fabricate high quality structures above the critical thickness. In this work, optical properties of alloyed InGaO NWs in a wide compositional range are carefully assessed. Unlike classical optical characterization methods, photoacoustic spectroscopy reveals the fundamental absorption edge despite the strong light scattering in porous and randomly oriented nanowires structure. An unusual compositional band gap dependence is also observed, giving insight into the phase segregation effect and increased quality of mixed NWs. In addition, photoacoustic measurements disclose potential applications of InGaO NWs in remote, light-driven loudspeakers because of intense photoacoustic effect in nanowire ensembles in this material system.

Recently, p-type metal–oxide–semiconductors have attracted considerable interests for the applications in optoelectronic devices and low-power complementary metal–oxide–semiconductor circuits. In this report, ternary p-type CuAlxOy semiconductor thin films were fabricated by sol–gel method and integrated as channel layers in thin-film transistors (TFTs). The electrical performances of CuAlxOy TFTs, together with the characteristics of CuAlxOy thin films (e.g., crystalline phases, chemical compositions, surface morphology, and optical transmittances), were systematically studied at various annealing temperatures ( ${T}_{a}$ ). The phase-pure CuAlO2 thin films were obtained at ${T}_{a}$ above 800° C in N2 atmosphere. CuAlO2 TFTs annealed at 900 ° C based on high-k Al2O3 exhibited optimized electrical performance, including a hole mobility of 1.36 cm2/Vs and on/off current ratio of $\sim 1 \times 10^{\textsf {5}}$ . This paper not only demonstrates the successful fabrication of high-quality p-type CuAlO2 semiconductor thin film and electronic devices by sol–gel process but also provides guidelines for related ternary p-type oxide semiconductor material and device performance improvements.

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.

The gallop of artificial intelligence ignites urgent demand on information processing systems with ultralow power consumption, reliable multi-parameter control and high operation efficiency. Here, the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) wrapped InGaAs nanowire (NW) artificial synapses capable to operate with record-low subfemtojoule power consumption are presented. The essential synaptic behaviors are mimicked and modulated effectively by adjusting the thickness of top modulation gate P(VDF-TrFE) films. Moreover, the long-term depression is realized by applying visible light (450 nm) because of the negative photoconductivity of InGaAs nanowires. Combined with optimal P(VDF-TrFE) films, the synaptic devices have the more linear long-term potentiation/depression characteristics and the faster supervised learning process simulated by hardware neural networks. The Pavlovian conditioning is also performed by combining electrical and infrared stimuli. Evidently, these ultralow-operating-power synapses are demonstrated with the brain-like behaviors, effective function modulation, and more importantly, the synergistic photoelectric modulation, which illustrates the promising potentials for neuromorphic computing systems.

Although In2O3 nanofibers (NFs) are well-known candidates as active materials for next-generation, low-cost electronics, these NF based devices still suffer from high leakage current, insufficient on–off current ratios (Ion/Ioff), and large, negative threshold voltages (VTH), leading to poor device performance, parasitic energy consumption, and rather complicated circuit design. Here, instead of the conventional surface modification of In2O3 NFs, we present a one-step electrospinning process (i.e., without hot-press) to obtain controllable Mg-doped In2O3 NF networks to achieve high-performance enhancement-mode thin-film transistors (TFTs). By simply adjusting the Mg doping concentration, the device performance can be manipulated precisely. For the optimal doping concentration of 2 mol%, the devices exhibit a small VTH (3.2 V), high saturation current (1.1 × 10–4 A), large on/off current ratio (>108), and respectable peak carrier mobility (2.04 cm2/(V·s)), corresponding to one of the best device performances among all 1D metal-oxide NFs based devices reported so far. When high-κ HfOx thin films are employed as the gate dielectric, their electron mobility and VTH can be further improved to 5.30 cm2/(V·s) and 0.9 V, respectively, which demonstrates the promising prospect of these Mg-doped In2O3 NF networks for highperformance, large-scale, and low-power electronics.

In this study, transparent p-type CuCrxOy semiconductor thin films were fabricated using spin coating and integrated as channel layers in thin-film transistors (TFTs). The structural, morphological components, and optical properties of CuCrxOy thin films, together with device performance, were systematically investigated. The phase conversion from a mixture of CuCr2O4 and CuO to pure CuCrO2 was achieved when the annealing temperature (Ta) was higher than 700 °C. The electrical performance of the CuCrxOy TFTs on SiO2 dielectric is improved with increasing Ta from 500 °C to 800 °C. The optimized CuCrO2 TFT exhibits an on/off current ratio of ∼105 and a hole mobility of 0.59 cm2 V−1 s−1, which is much better than those previous works on solution-processed binary CuxO TFTs. To our best knowledge, this work demonstrates the ternary p-type CuCrO2 TFTs fabricated via a low-cost solution process for the first time, which represents an important advancement towards the development of all-oxide, low-cost p–n junctions and CMOS logic circuits.

One-dimensional (1D) nanofibers have been considered to be important building blocks for nano-electronics due to their superior physical and chemical properties. In this report, high-performance zinc tin oxide (ZnSnO) nanofibers with various composition ratios were prepared by electrospinning. The surface morphology, crystallinity, grain size distribution, and chemical composition of the nanofibers were investigated. Meanwhile, field-effect transistors (FETs) based on ZnSnO nanofiber networks (NFNs) with various composition ratios were integrated and investigated. For optimized Zn0.3Sn0.7O NFNs FETs, the device based on an SiO2 dielectric exhibited a high electrical performance, including a high on/off current ratio (Ion/off) of 2 × 107 and a field-effect mobility (μFE) of 0.17 cm2 V-1 s-1. When a high-permittivity (κ) ZrOx thin film was employed as the dielectric in Zn0.3Sn0.7O NFNs FETs, the operating voltage was substantially reduced and a high μFE of 7.8 cm2 V-1 s-1 was achieved. These results indicate that the Zn0.3Sn0.7O NFNs/ZrOx FETs exhibit great potency in low-cost and low-voltage devices.

High permittivity (high k) metal-oxide thin films fabricated via solution processes have recently received much attention for the construction of low-operating voltage and high-performance thin-film transistors (TFTs). In this report, amorphous ytterbium oxide (Yb2O3) thin films were fabricated by spin coating and their applications in TFTs were explored. The physical properties of the solution-processed Yb2O3 thin films processed at different annealing temperatures were systematically investigated using various characterization techniques. To explore the feasibility of the Yb2O3 thin films as gate dielectrics for oxide TFTs, In2O3 TFTs based on Yb2O3 dielectrics were integrated. All the devices could be operated at 3 V, which is critical for the applications in portable, battery-driven, and low-power electronic devices. The optimized In2O3/Yb2O3 TFT exhibits high electrical performances, including field-effect mobility of 4.98 cm2/V s, on/off current ratio of ~ 106, turn-on voltage around 0 V, and subthreshold swing of 70 mV/decade, respectively. To demonstrate the potential of In2O3/Yb2O3 TFT toward more complex logic application, the unipolar inverter was further constructed.

In this paper, high-k strontium oxide (SrOx) dielectric thin films were fabricated using simple and low-cost solution process. The formation and properties of SrOx thin films annealed at various temperatures (400 °C, 500 °C, 600 °C, and 700 °C) were investigated using numbers of characterization techniques. The electrical analysis indicates that the insulating properties of SrOx thin films were improved with increasing annealing temperature. The post-annealing at temperatures higher than 400 °C enables the SrOx thin film, exhibiting low-leakage current density of ~10−8 A cm−2 at 3 V and the areal capacitance larger than 350 nF cm−2 at 20 Hz. To further explore the possible applications of solution-processed high-k SrOx thin films for thin-film transistors (TFTs), the indium oxide (In2O3) TFTs based on SrOx thin films were integrated for testing. The optimized In2O3/SrOx TFT exhibits high performance with an average field-effect mobility of 5.61 cm2 V−1 s−1, a small subthreshold swing of 110 mV dec−1, and a large on/off current ratio of 107. To demonstrate the potential of In2O3/SrOx TFT toward more complex logic applications, the unipolar inverter was further constructed and exhibited a high gain of 9.7. Importantly, all these device parameters were obtained at an ultralow operating voltage of 3 V, which represents a step toward portable, battery-driven, and low-power consumption electronics and circuits.

One-dimensional metal-oxide nanowires are regarded as important building blocks in nanoscale electronics, because of their unique mechanical and electrical properties. In this work, p-type nickel oxide nanowires (NiO NWs) were fabricated by combining sol-gel and electrospinning processes. The poly(vinylpyrrolidone) (PVP) with a molecular weight of 1 300 000 was used as the polymer matrix to increase the viscosity of a NiO precursor solution. The formation and properties of the as-spun NiO/PVP composite NWs before/after calcination treatment were investigated using various techniques. Because of the enhanced adhesion properties between ultraviolet (UV)-treated NiO NWs and the substrate, the field-effect transistors (FETs) based on NiO NWs were found to exhibit satisfying p-channel behaviors. For the fabrication of aligned NiO NW arrays, two parallel conducting Si strips were grounded as NW collector. The integrated FETs based on aligned NiO NWs were demonstrated to exhibit superior electrical performance, compared to the disordered counterparts with the comparable NW coverage. By employing high- k aluminum oxide (Al

Electrospun metal oxide nanofibers have been regarded as promising blocks for large-area, low-cost, and one-dimensional electronic devices. However, the electronic devices based on electrospun nanofibers usually suffer from poor performance and inferior viability. Here, we report an efficient photochemical process using UV light generated by a high-pressure mercury lamp to promote the electrical performance of the nanofiber-based electronic devices. Such UV treatment can lead to strong photochemical activation of electrospun nanofibers, and therefore, a stable adherent nanofiber network and electronic-clean interface were formed. By use of UV treatment, high-performance indium oxide (In2O3) nanofiber based field-effect transistors (FETs) with highly efficient modulation of electrical characteristics have been successfully fabricated. To reduce the operating voltage and further improve the device performance, the In2O3 nanofiber FETs based on solution-processed high-k AlOx dielectrics were integrated and i...

Although there are recent advances in many areas of quasi-2D halide perovskites, photodetectors based on these materials still cannot achieve satisfactory performance for practical applications where high responsivity, fast response, self-powered nature, and excellent mechanical flexibility are urgently desired. Herein, utilizing one-step spin-coating method, self-assemble quasi-2D perovskite films with graded phase distribution in the order of increasing number of metal halide octahedral layers are successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained and then employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibits impressive performance with the responsivity up to 444 mA W-1 and ultrashort response time down to 52 µs. With a bias voltage of 1.5 V, the device responsivity becomes 3463 mA W-1 with the response speed as fast as 24 µs. Importantly, the device's mechanical flexibility is greatly enhanced since the photocurrent prefers flowing through the metal halide octahedral layers between the top and bottom contact electrodes in the vertical device structure, being more tolerant to film damage. These results evidently indicate the potential of graded quasi-2D perovskite phases for next-generation optoelectronic devices.

The fabrication of water-induced amorphous high-k zirconium oxide (ZrOx) dielectrics has been proposed with the objective of achieving high performance and reducing costs for next generation displays. In this study, the as-prepared ZrOx thin films were fabricated by a sequential process, including a UV-assisted photochemical treatment and a thermal annealing process at temperatures lower than 300 °C. It is observed that the leakage current density of ZrOx thin films decreases, and the capacitance increases with increasing annealing temperatures. To verify the application possibilities of ZrOx thin films as gate dielectrics in complementary metal-oxide semiconductor (CMOS) electronics, both n-type In2O3 and p-type NiOx channel layers were integrated with ZrOx dielectrics and their corresponding electrical performances were examined. The In2O3/ZrOx thin film transistor (TFT) annealed at 250 °C exhibited a high electron mobility of 10.78 cm2 V−1 s−1, a small subthreshold swing of 75 mV dec−1, and a large on–off current ratio (Ion/Ioff) of around 106, respectively. Moreover, the p-type NiOx/ZrOx TFT exhibited an Ion/Ioff of 105 and a hole mobility of 4.8 cm2 V−1 s−1. It is noted that both n- and p-channel oxide TFTs on ZrOx could be operated at voltages lower than 4 V. The low-temperature fabrication process marks a great step towards the further development of low-cost, all-oxide CMOS electronics on flexible substrates.

Recently, semiconducting nanofiber networks (NFNs) have been considered as one of the most promising platforms for large-area and low-cost electronics applications. However, the high contact resistance among stacking nanofibers remained to be a major challenge, leading to poor device performance and parasitic energy consumption. In this report, a controllable welding technique for NFNs was successfully demonstrated via a bioinspired capillary-driven process. The interfiber connections were well-achieved via a cooperative concept, combining localized capillary condensation and curvature-induced surface diffusion. With the improvements of the interfiber connections, the welded NFNs exhibited enhanced mechanical property and high electrical performance. The field-effect transistors (FETs) based on the welded Hf-doped In2O3 (InHfO) NFNs were demonstrated for the first time. Meanwhile, the mechanisms involved in the grain-boundary modulation for polycrystalline metal-oxide nanofibers were discussed. When the high-k ZrO x dielectric thin films were integrated into the FETs, the field-effect mobility and operating voltage were further improved to be 25 cm2 V-1 s-1 and 3 V, respectively. This is one of the best device performances among the reported nanofibers-based FETs. These results demonstrated the potencies of the capillary-driven welding process and grain-boundary modulation mechanism for metal-oxide NFNs, which could be applicable for high-performance, large-scale, and low-power functional electronics.

Technical development for thin-film fabrication is essential for emerging metal-oxide (MO) electronics. Although impressive progress has been achieved in fabricating MO thin films, the challenges still remain. Here, we report a versatile and general thermal-induced nanomelting technique for fabricating MO thin films from the fiber networks, briefly called fiber-to-film (FTF) process. The high quality of the FTF-processed MO thin films was confirmed by various investigations. The FTF process is generally applicable to numerous technologically relevant MO thin films, including semiconducting thin films (e.g., In2O3, InZnO, and InZrZnO), conducting thin films (e.g., InSnO), and insulating thin films (e.g., AlOx). By optimizing the fabrication process, In2O3/AlOx thin-film transistors (TFTs) were successfully integrated by fully FTF processes. High-performance TFT was achieved with an average mobility of ∼25 cm2/(Vs), an on/off current ratio of ∼107, a threshold voltage of ∼1 V, and a device yield of 100%. As...

In this work, we develop a simple and eco-friendly water-inducement method for high-k yttrium oxide (YOx) dielectric. To prepare YOx thin films at low temperature, yttrium nitrate and deionized water were used as the source materials. No toxic organic materials were required in the YOx coating process. The YOx thin film annealed at 350 � C showed a low leakage current density of 2 � 10 � 9 A/cm 2 at 5 MV/cm and a large areal-capacitance of 448 nF/cm 2 at 1 kHz. On the basis of its implementation as the gate dielectric, the fully-water-induced In2O3 TFT based on YOx exhibited a high field-effect mobility of 15.98 cm 2 /Vs, excellent subthreshold swing of 75 mV/dec, an on/off current ratio of 6 � 10 6 , and a negligible hysteresis of 50 mV. The as-fabricated TFT operated at a low voltage (~1.5 V) and showed high drain current drive capability, enabling oxide TFT with a water-induced high-k dielectric for use in backplane electronics for low-power mobile display applications.

Copper oxide (CuxO) thin films were fabricated on SiO2/Si substrates by using a solution process. The coated CuxO gel films were treated using a vacuum annealing method at various temperatures (400–700 °C). X-ray diffraction results indicated that the vacuum annealing technique was effective in transforming CuO into Cu2O. Atomic force microscopy images showed that the mean grain size and the surface roughness of the resulting films increased with increasing annealing temperature. To verify the possibility of CuxO thin films as channel layers, the bottom gate structured thin film transistors (TFTs) were integrated. The electrical properties of the as-fabricated CuxO TFTs were improved with increasing processing temperature from 400 to 600 °C. The 600 °C-annealed CuxO TFT exhibited the best electrical performances, including a low threshold voltage of −3.2 V, a large field-effect mobility of 0.29 cm2 V−1 s−1, a small subthreshold swing of 0.8 V dec−1, and an on/off current ratio of 1.6 × 104, respectively. However, with increasing annealing temperature, the electrical properties of the CuxO TFTs were degraded dramatically. These results suggest that solution-processed CuxO TFTs achieved by using a one-step vacuum annealing technique could potentially be used for high-performance p-type electronic devices, which represents a great step towards the further development of low-cost and all-oxide CMOS electronics.

In this study, indium oxide (In2O3) thin-film transistors (TFTs) were fabricated by a solution-process at low temperature. A single precursor in a single solvent system was used as the In2O3 precursor to minimize the carbon-based impurities. The 300 °C-annealed In2O3 TFT with channel thickness of 12 nm exhibits enhanced performance, which shows saturation mobility (μsat) of 3.08 cm2 V−1 s−1, an on/off current ratio (Ion/Ioff) of 1.04 × 108, a threshold voltage (VT) of 12.7 V, and a subthreshold swing (SS) of 1.49 V per decade. Finally, high-performance In2O3 TFT based on solution-processed zirconium oxide dielectric was realized, which shows distinguished electrical performance (μsat = 13.01 cm2 V−1 s−1, Ion/Ioff = 1.09 × 107, VT = 1.2 V, and SS = 0.1 V per decade). These results suggest that solution-processed In2O3 TFTs could potentially be used for low-cost, low-temperature, and high-performance electronic devices.

Low-temperature solution processing opens a new window for the fabrication of oxide semiconductors due to its simple, low cost, and large-area uniformity. Herein, by using solution combustion synthesis (SCS), p-type Cu-doped NiO (Cu:NiO) thin films are fabricated at a temperature lower than 150 °C. The light doping of Cu substitutes the Ni site and disperses the valence band of the NiO matrix, leading to an enhanced p-type conductivity. Their integration into thin-film transistors (TFTs) demonstrates typical p-type semiconducting behavior. The optimized Cu5% NiO TFT exhibits outstanding electrical performance with a hole mobility of 1.5 cm2 V-1 s-1 , a large on/off current ratio of ≈104 , and clear switching characteristics under dynamic measurements. The employment of a high-k ZrO2 gate dielectric enables a low operating voltage (≤2 V) of the TFTs, which is critical for portable and battery-driven devices. The construction of a light-emitting-diode driving circuit demonstrates the high current control capability of the resultant TFTs. The achievement of the low-temperature-processed Cu:NiO thin films via SCS not only provides a feasible approach for low-cost flexible p-type oxide electronics but also represents a significant step toward the development of complementary metal-oxide semiconductor circuits.

Recently, indium oxide (In2O3) semiconducting nanowires (NWs) have been extensively explored as building blocks for numerous electronic applications. However, most of the field-effect transistors (FETs) based on In2O3 NWs were operated in depletion mode (D-mode), which exhibits negative threshold voltage (V TH) and non-zero current with zero bias. Besides, these devices based on In2O3 NWs still suffer from high leakage current and low on-off current ratios (I on/off). In this report, high-performance enhancement-mode (E-mode) FETs based on Ti doped In2O3 NWs were successfully integrated. It was found that the device performance could be effectively modulated by adjusting the doping concentration of Ti. The FETs based on In2O3 NWs with Ti doping concentration of 3 mol% exhibited a saturation current of 4.69 × 10−4 A, a subthreshold swing (SS) of 1.54 V/decade, an on/off current ratio of ~1.5 × 108, and a field-effect mobility of 2.53 cm2 V−1 s−1. When high-κ ZrO x dielectrics were successfully integrated into the FETs, the mobility and SS of the designed device were improved to 12.67 cm2 V−1 s−1 and 150 mV/decade, respectively. The inverters based on InTiO NWs/ZrO x FETs were constructed and showed a gain of ~9.5. All of these results demonstrate that Ti-doped In2O3 NWs are promising candidates for large-scale, high-performance and low-power electronic devices.

This study was supported by the Natural Science Foundation of China (Grant Nos. 51472130, 51672142, and 51572135). Solution-processed metal-oxide thin films with high dielectric constants (k) have been extensively studied for low-cost and high-performance thin-film transistors (TFTs). In this report, MgO dielectric films were fabricated using the spin-coating method. The MgO dielectric films annealed at various temperatures (300, 400, 500, and 600 °C) were characterized by using thermogravimetric analysis, optical spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic-force microscopy. The electrical measurements indicate that the insulating properties of MgO thin films are improved with an increase in annealing temperature. In order to clarify the potential application of MgO thin films as gate dielectrics in TFTs, solution-derived In2O3 channel layers were separately fabricated on various MgO dielectric layers. The optimized In2O3/MgO TFT exhibited an electron mobility of 5.48 cm2/V s, an on/off current ratio of 107, and a subthreshold swing of 0.33 V/dec at a low operation voltage of 6 V. This work represents a great step toward the development of portable and low-power consumption electronics. publishersversion published

One-dimensional metal oxide nanofibers have been regarded as promising building blocks for large area low cost electronic devices. As one of the representative metal oxide semiconducting materials, In2O3 based materials have attracted much interest due to their excellent electrical and optical properties. However, most of the field-effect transistors (FETs) based on In2O3 nanofibers usually operate in a depletion mode, which lead to large power consumption and a complicated integrated circuit design. In this report, gadolinium (Gd) doped In2O3 (InGdO) nanofibers were fabricated by electrospinning and applied as channels in the FETs. By optimizing the doping concentration and the nanofiber density, the device performance could be precisely manipulated. It was found that the FETs based on InGdO nanofibers, with a Gd doping concentration of 3% and a nanofiber density of 2.9 μm−1, exhibited the best device performance, including a field-effect mobility (μFE) of 2.83 cm2/V s, an on/off current ratio of ∼4 × 108, a threshold voltage (VTH) of 5.8 V, and a subthreshold swing (SS) of 2.4 V/decade. By employing the high-k ZrOx thin films as the gate dielectrics in the FETs, the μFE, VTH and SS can be further improved to be 17.4 cm2/V s, 0.7 V and 160 mV/decade, respectively. Finally, an inverter based on the InGdO nanofibers/ZrOx FETs was constructed and a gain of ∼11 was achieved.

Although significant progress has been made towards using ZnO nanofibers (NFs) in future high-performance and low-cost electronics, they still suffer from insufficient device performance caused by substantial surface roughness (i.e., irregularity) and granular structure of the obtained NFs. Here, a simple one-step electrospinning process (i.e., without hot-press) is presented to obtain controllable ZnO NF networks to achieve high-performance, large-scale, and low-operating-power thin-film transistors. By precisely manipulating annealing temperature during NF fabrication, their crystallinity, grain size distribution, surface morphology, and corresponding device performance can be regulated reliably for enhanced transistor performances. For the optimal annealing temperature of 500 degrees C, the device exhibits impressive electrical characteristics, including a small positive threshold voltage (V-th) of approximate to 0.9 V, a low leakage current of approximate to 10(-12) A, and a superior on/off current ratio of approximate to 10(6), corresponding to one of the best-performed ZnO NF devices reported to date. When high- AlOx thin films are employed as gate dielectrics, the source/drain voltage (V-DS) can be substantially reduced by 10x to a range of only 0-3 V, along with a 10x improvement in mobility to a respectable value of 0.2 cm(2) V-1 s(-1). These results indicate the potential of these nanofibers for use in next-generation low-power devices.

In this study, we report high-performance amorphous In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using an ultra-thin solution-processed amorphous ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick amorphous layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). Apart from that we obtain an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, and a voltage shift ≤ 0.4 V under positive bias stress for 2.5 h, for a gate voltage of 3 V and drain voltage of 1 V. These data demonstrate that the BMO TFT has great potential for a broad range of applications as switching low-power transistors.

We report continuous-wave laser operation at 698 nm in Pr3+-doped LiYF4 crystal using an InGaN laser diode emitting at 444 nm with a maximum output power of 760 mW. By suppressing the oscillation at 640 and 721 nm, a maximum output power of 156 mW at 698 nm was obtained in a single transverse mode with a slope efficiency as high as 48.7%. The beam quality factors M2 in the x and y directions were measured to be 1.4 and 1.2, respectively.