Improved Carrier Mobility Research Articles

Silver Telluride Colloidal Quantum Dot Solid for Fast Extended Shortwave Infrared Photodetector.

Extended shortwave infrared (eSWIR) photodetectors that employ solution-processable semiconductors have attracted attention for use in applications such as ranging, night vision, and gas detection. Colloidal quantum dots (CQDs) are promising materials with facile bandgap tunability across the visible-to-mid-infrared wavelengths. However, toxic elements, such as Hg and Pb, and the slow response time of CQD-based IR photodetectors, limit their commercial viability. This article presents a novel eSWIR photodetector that is fabricated using silver telluride (Ag2Te) CQDs. Effective thiolate ligand exchange enables a lower trap density and improved carrier mobility in CQD solids. Furthermore, a vertical p-n photodiode architecture with a favorable energy-level landscape is utilized to facilitate charge extraction, resulting in a fast, room-temperature-operable, and toxic-element-free CQD photodetector. The best eSWIR Ag2Te CQD photodetector exhibits a fall time of 72ns, representing the fastest response time among all prior CQD-based eSWIR photodetectors, including those containing toxic elements, such as Pb and Hg.

Cryogenic temperature operation of NiO/Ga2O3 heterojunction and Ni/Au Schottky rectifiers

Vertical geometry NiO/Ga2O3 heterojunction (HJ) rectifiers and Ni/Au Schottky rectifiers fabricated on the same wafer and each with the same diameter (100 μm) were operated at 77–473 K to compare their capabilities in space-like environments. The HJ rectifiers suffer a 4-order reduction in forward current at 77 K due to the freeze-out of acceptors in the NiO, leading to MIS-type operation. By sharp contrast, the Schottky rectifiers have higher forward current and lower on-resistance at 77 K compared to 298 K due to improved carrier mobility. The on/off ratio of Schottky rectifiers at 77 K becomes similar to HJ rectifiers at 298–473 K. The reverse recovery time of Schottky rectifiers is reduced from 20 ns at 273 K to 16 ns at 77 K, while HJ rectifiers cannot be switched at this temperature. While the latter are superior for high-temperature applications, the former are better suited to cryogenic operation.

Amorphous InZnSnO thin-film-transistors performance enhancement with low-energy Xenon Pulsed-light annealing

The electrical characteristics and stability of amorphous indium-zinc-tin oxide (IZTO) thin-film transistors (TFTs) were significantly improved in this study using low-energy Xenon pulsed-light annealing (PLA). In comparison to conventional furnace annealing (FA), PLA treatment significantly reduced the processing temperature and annealing time. Besides, the defect states are obviously reduced from 1.73×1012 cm-2 to 6.53×1011 cm-2 by PLA treatment, resulting in improved device electrical characteristics and enhanced reliability, including improved carrier mobility from 20.08 to 39.61 cm2/V∙s, threshold voltage from 0.82 to 0.24 V, subthreshold swing (S.S.) from 0.54 to 0.24 V/decade, and the ON/OFF current ratio from 2.32×107 to 7.31×108. In addition, the enhanced stability is observed under both positive gate-bias stress (PGBS) of VGS = 30 V and negative gate-bias stress (NGBS) of VGS = –30 V for a stress duration of 3000 s. The threshold voltage shift (ΔVTH) is reduced from 8.31 V to 1.65 V and from –3.93 V to –1.51 V, respectively. This is the first time low-energy PLA was conducted for IZTO TFT performance improvement.

On the Bulk Photovoltaic Effect in the Characterization of Strained Germanium Microstructures

Strain engineering serves as an effective method for optimizing electronic and optical properties in semiconductor devices, with applications including the enhancement of optical emission in Ge and GeSn‐based devices, improvement of carrier mobility, and second harmonic generation in silicon photonics structures. Current methods for deformation characterization in semiconductors, such as X‐ray diffraction and Raman spectroscopy, often require bulky and expensive setups and are limited in vertical resolution. Consequently, techniques capable of measuring lattice strain while overcoming these drawbacks are highly desirable. This study proposes a proof of concept for a cost‐effective, compact, fast, and non‐destructive approach to probe non‐uniform strain fields and additional material properties by exploiting the bulk photovoltage effect. The method is benchmarked with an array of silicon nitride stripes deposited under varying pressure conditions on a germanium substrate. Initially, their surface strains are verified through Raman spectroscopy. The deformations are replicated in a finite element method platform by integrating mechanical simulations with deformation potential theory, thereby estimating the band edge energy landscape. Finally, the study discusses the theoretical behavior of the photovoltage signal, considering semiconductor properties, defects, doping, and deformation. The findings offer insights into the development of advanced techniques for strain and transport analysis in semiconductor materials.

Low-Defect-Density Monolayer MoS2 Wafer by Oxygen-Assisted Growth-Repair Strategy.

Atomic chalcogen vacancy is the most commonly observed defect category in two dimensional (2D) transition-metal dichalcogenides, which can be detrimental to the intrinsic properties and device performance. Here a low-defect density, high-uniform, wafer-scale single crystal epitaxial technology by in situ oxygen-incorporated "growth-repair" strategy is reported. For the first time, the oxygen-repairing efficiency on MoS2 monolayers at atomic scale is quantitatively evaluated. The sulfur defect density is greatly reduced from (2.71 ± 0.65) × 1013 down to (4.28 ± 0.27) × 1012 cm-2, which is one order of magnitude lower than reported as-grown MoS2. Such prominent defect deduction is owing to the kinetically more favorable configuration of oxygen substitution and an increase in sulfur vacancy formation energy around oxygen-incorporated sites by the first-principle calculations. Furthermore, the sulfur vacancies induced donor defect states is largely eliminated confirmed by quenched defect-related emission. The devices exhibit improved carrier mobility by more than three times up to 65.2 cm2 V-1 s-1 and lower Schottky barrier height reduced by half (less than 20 meV), originating from the suppressed Fermi-level pinning effect from disorder-induced gap state. The work provides aneffective route toward engineering the intrinsic defect density and electronic states through modulating synthesis kinetics of 2D materials.

Impact of the alkyl side-chain length on solubility, interchain packing, and charge-transport properties of amorphous π-conjugated polymers

Increasing the length of alkyl side chains is a typical way to improve the solubility of π-conjugated polymers designed for use in solution-processed devices. However, these modifications have also been reported to alter the film morphology. Given that the mechanism leading to improved solubility is not well documented yet and the nanoscale (local) morphologies of amorphous π-conjugated polymer films are difficult to characterize experimentally, here, we combine molecular dynamics simulations and long-range corrected density functional theory calculations to examine at the molecular scale the impact that the alkyl side-chain length has on polymer solubility and film morphologies. As a representative example, we consider poly(thieno[3,4-c]pyrrole-4,6-dione-alt-3,4-difluorothiophene) (PTPD[2F]T) with two different lengths of the alkyl side chains on the thieno[3,4-c]pyrrole-4,6-dione (TPD) moieties, i.e., 2-hexyldecyl (2HD) and 2-decyltetradecyl (2DT). A detailed analysis of polymer–solvent and polymer–polymer interactions provides a picture that describes the underlying mechanism for improved solubility in going from 2HD to 2DT. We then underline an intrinsic characteristic that decreasing the side-chain length brings a greater extent of backbone planarity and lesser side chain-TPD interactions, which leads to higher interchain π-π packing density and order, while the interchain π-π packing patterns remain similar in the two films. These morphologies are discussed in terms of the charge-transport properties between neighboring PTPD[2F]T chains, which point to a higher electron mobility in the PTPD[2F]T films with shorter alkyl side chains. Overall, our findings offer guidance in the field of solution-processed electronic devices by pointing out that the polymer alkyl side-chain length could be minimized to improve carrier mobility while ensuring polymer solubility.

Electric wind induced texturing for enhanced thermoelectric performance of p-type Mg3Sb2-based materials

High-intensity electric pulse treatment (EPT) can induce electric wind effect in materials, which facilitates the grain rearrangement and reorientation in polycrystalline samples. For the first time, this study employed the EPT technique to construct texture in Mg3.04Ag0.02Sb2 bulk compounds, and a highly conductive channel was produced to promote the charge carrier transport. This leads to a 53 % improvement in carrier mobility of the EPT sample (4#20) over the pristine one at room temperature. Additionally, EPT does not affect the carrier concentration of the material, making the EPT samples possess significantly improved electrical conductivities and untouched Seebeck coefficients. Consequently, a 36 % improvement in zT value is achieved for the EPT sample (4#20) at 723 K, compared to the pristine one. This work demonstrates that EPT technique is an effective approach for constructing textured Mg3Sb2-based materials, offering a valuable avenue for high thermoelectric performance in other potential materials via manipulating properties-related texture.

Enhancing the Electrical Conductivity and Long-Term Stability of PEDOT:PSS Electrodes through Sequential Treatment with Nitric Acid and Cesium Chloride.

Solution-processable poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is an important polymeric conductor used extensively in organic flexible, wearable, and stretchable optoelectronics. However, further enhancing its conductivity and long-term stability while maintaining its superb mechanical properties remains challenging. Here, a novel post-treatment approach to enhance the electrical properties and stability of sub-20-nm-thin PEDOT:PSS films processed from solution is introduced. The approach involves a sequential post-treatment with HNO3 and CsCl, resulting in a remarkable enhancement of the electrical conductivity of PEDOT:PSS films to over 5500 S cm-1, along with improved carrier mobility. The post-treated films exhibit remarkable air stability, retaining over 85% of their initial conductivity even after 270 days of storage. Various characterization techniques, including X-ray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy, Hall effect measurements, and grazing incidence wide angle X-ray scattering, coupled with density functional theory calculations, provide insights into the structural changes and interactions responsible for these improvements. To demonstrate the potential for practical applications, the ultrathin PEDOT:PSS films are connected to an inorganic light-emitting diode with a battery, showcasing their suitability as transparent electrodes. This work presents a promising approach for enhancing the electrical conductivity of PEDOT:PSS while offering a comprehensive understanding of the underlying mechanisms that can guide further advances.

The impact of series ([formula omitted]) and shunt resistances ([formula omitted]) on solar cell parameters to enhance the photovoltaic performance of f-PSCs

Flexible Perovskite Solar Cells (f-PSCs) are made on an ITO-coated PET substrate. SnO2 has been used as a transparent inorganic electron transporting layer (ETL), PEDOT: PSS as an organic hole transporting layer (HTL), and C H3 N H3 Pb I3 as a perovskite absorbing layer. Two configurations of the device structure have been formed, one is normal structure ITO/PET/ SnO2/C H3 N H3 Pb I3/PEDOT: PSS/Ag (n-i-p) and the other is inverted structure ITO/PET/PEDOT: PSS/C H3 N H3 Pb I3/ SnO2/Ag (p-i-n). An antisolvent (i.e. ethyl acetate) has been used to control the surface morphology of the perovskite layers during fabrication of f-PSCs. Applying antisolvent in perovskite improves carrier mobility, transport properties, and higher power conversion efficiency (PCE) achieved. This study focuses on the effects of series (Rs) and shunt resistance (Rsh) of f-PSCs on photovoltaic parameters while controlling the surface morphology of perovskite films applied on both structures. The study examines the behaviour of f-PSCs with and without the use of an antisolvent. For normal structure, PCE is found at 11.34 % for f-PSCs with antisolvent and 7.96 % for f-PSCs without antisolvent. On the other hand, inverted structures show PCE 10.36 % and 7.46 % for f-PSCs with and without antisolvent, respectively. PCE has been calculated for the f-PSCs by bending the samples about 3 0o angle and about 20 % decrease in PCE has been found. The oddity of this work is to estimate the series and shunt resistant for f-PSCs and find the cost-effective control of these parameters by controlling interfacial defects.

Organic-Inorganic Rubrene/WS2 Heterostructure for Broadband Detection and Polarization Imaging.

Organic single crystals exhibit improved carrier mobility, longer exciton diffusion length, anisotropic charge transport, and unique linear dichroism, while its high exciton binding energy seriously limits the free-carrier generation and photoelectric conversion efficiency. Layered van der Waals heterostructures, which integrate organic crystals with high mobility two-dimensional (2D) inorganic semiconductors, are promising for promoting exciton dissociation and boosting sensitivity by utilizing the interfacial potential and photogating effect. In this work, organic single-crystal rubrene is integrated with a few-layer WS2 to design the high-performance photodetector. The device exhibits an excellent responsivity of 1000 A W-1, and a fast speed of 180 μs, which is far superior to the individual WS2 device. Equally importantly, this device provides excellent polarization detection performance by virtue of the anisotropic properties of rubrene, and the dichroic ratios are 1.56, 1.5, and 1.7 for 375, 405, and 658 nm irradiation, respectively. Finally, several high-resolution single-pixel broadband polarization imaging was demonstrated. Our work shows that organic-inorganic heterostructure is an essential candidate for improving optoelectronics performance and has potential for polarization imaging.

Enhancement in Sensitivity and Selectivity of Electrochemical Technique with CuO/g-C3N4 Nanocomposite Combined with Molecularly Imprinted Polymer for Melamine Detection.

This study focused on enhancing the sensitivity and selectivity to detect melamine by utilizing a photoelectrochemical method. This was achieved by combining a melamine-imprinted polymer with a CuO/g-C3N4 nanocomposite, which was synthesized through chemical precipitation and calcination. The resulting nanocomposite exhibits improved carrier mobility and photoelectrochemical properties. A molecularly imprinted receptor for selective detection was created through bulk polymerization with methacrylic acid and a melamine template. The characterization of the nanocomposite was performed using X-ray photoelectron spectroscopy for the chemical oxidation state, X-ray diffraction patterns for the crystalline structure, and ultraviolet/visible/near-infrared spectroscopy for optical properties. The CuO/g-C3N4 nanocomposite exhibits photoactivity under visible light. The modified electrode, incorporating the CuO/g-C3N4 nanocomposite and melamine-imprinted polymer, demonstrates a linear detection range of 2.5 to 50 nM, a sensitivity of 4.172 nA/nM for melamine, and a low detection limit of 0.42 nM. It shows good reproducibility and high selectivity to melamine, proving effective against interferences and real samples, showcasing the benefits of the molecularly imprinted polymer.

Unraveling Dual Mechanisms in Quasi‐Layered Bi2O2Se via Defect Modulation for High‐Performance Aqueous Zn‐Ion Batteries

AbstractDeveloping cathode materials for aqueous zinc‐ion batteries (ZIBs) that offer high capacity, rapid charge–discharge rates, and prolonged cycle life remains a significant challenge. This study explores the use of zipper‐type Bi2O2Se nanoplates modified by selenium vacancy (Vse) modulation, which reduces electron scattering, enhances carrier mobility in [Bi2O2] conducting channels, and decreases coulombic interactions within electrostatic layers. The introduction of Se vacancies facilitates electron transfer from the host to [Bi2O2] channels and reduces scattering in the [Bi2O2] framework, thus improving carrier mobility. These Se‐poor Bi2O2Se nanoplates demonstrate a greater affinity for zinc ions, reduced diffusion barriers, and faster transport kinetics, which enable more efficient Zn‐ion insertion, tripling the electrochemical capacity, improving rate capabilities, and extending cycling life. Enhancements such as reinforced structural integrity and expanded interlayer spaces support a dual Zn‐ion‐driven mechanism involving both insertion and conversion reactions, essential for superior electrochemical storage performance. The results include an impressive discharge/charge capacity of 380.3 mA h g−1 at 0.1 A g−1, a cycle life of up to 10 000 cycles at 5 A g−1, and a current tolerance exceeding 10 A g−1. This research highlights how nano‐ and defect engineering of Bi2O2Se can significantly enhance ionic conductivity, expedite electron transfer, and improve Zn‐ion diffusion.

Counter-Doping Effect by Trivalent Cations in Tin-Based Perovskite Solar Cells.

Tin (Sn) -based perovskite solar cells (PSCs) normally show low open circuit voltage due to serious carrier recombination in the devices, which can be attributed to the oxidation and the resultant high p-type doping of the perovskite active layers. Considering the grand challenge to completely prohibit the oxidation of Sn-based perovskites, a feasible way to improve the device performance is to counter-dope the oxidized Sn-based perovskites by replacing Sn2+ with trivalent cations in the crystal lattice, which however is rarely reported. Here, the introduction of Sb3+, which can effectively counter-dope the oxidized perovskite layer and improve the carrier lifetime, is presented. Meanwhile, Sb3+ can passivate deep-level defects and improve carrier mobility of the perovskite layer, which are all favorable for the photovoltaic performance of the devices. Consequently, the target devices yield a relative enhancement of the power conversion efficiency (PCE) of 31.4% as well as excellent shelf-storage stability. This work provides a novel strategy to improve the performance of Sn-based PSCs, which can be developed as a universal way to compensate for the oxidation of Sn-based perovskites in optoelectronic devices.

Improvement of Carrier Mobility in Quantum Wells by the Surface Smoothing of Strain-Relaxed Buffer Layers

Improvement of Carrier Mobility in Quantum Wells by the Surface Smoothing of Strain-Relaxed Buffer Layers

Theoretical design of Sc2CF2/Ti2CO2 heterostructure as a promising direct Z-scheme photocatalyst towards efficient water splitting

Van der Waals (vdW) heterostructure catalysts with the direct Z-scheme charge transfer path are highly expected for photocatalytic water splitting to address the energy crisis. In this work, the novel Sc2CF2/Ti2CO2 heterostructure has been developed and its photocatalytic utility was evaluated based on the first-principles method. Results indicate the heterostructure is an indirect semiconductor with improved carrier mobilities and absorption. The transfer of photogenerated carriers in this heterostructure follows the Z-scheme path, and the band edge positions confirm its suitability for water splitting. More importantly, the change in Gibbs free energy indicates that solar energy can drive water splitting in Sc2CF2/Ti2CO2 heterostructure with an attractive solar-to-hydrogen efficiency of 41.7%. Besides, biaxial tensile strain can turn Sc2CF2/Ti2CO2 heterostructure into a direct semiconductor, while its photocatalytic performance can be improved. In brief, all findings prove the potential of Sc2CF2/Ti2CO2 heterostructure as a promising direct Z-scheme photocatalyst for efficient water splitting.

Optimizating TiO2 electron transport layer for MAPbBr3 perovskite solar cells by way of Ga doping

The exceptional electron transport performance and high stability of titanium dioxide (TiO2) make it widely used in the electron transport layer (ETL). However, the presence of numerous surface defects in TiO2 layer can lead to unnecessary non-radiative recombination, which reduces carrier mobility and affects the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs). Therefore, tremendous researches have been focused on reducing surface defects and improving carrier mobility in TiO2 layer. In this study, we adopted metal gallium (Ga) with high conductivity at room temperature as an optimization strategy to enhance the performance of TiO2 layer. By incorporating metal Ga into the TiO2 precursor solution, we successfully fabricated a TiO2-Ga layer that exhibits reduced surface defects and optimized energy level structure. This provides an efficient pathway for electron transport in perovskite layer. Experimental results demonstrate that (methyl ammonium lead tribromide) MAPbBr3 perovskite solar cell devices based on TiO2-Ga layer achieve nearly 24% higher PCE compared to those based on pure TiO2 layer. This successful optimization strategy utilizing metal Ga offers novel insights and approaches for enhancing the performance of PSCs.

Manipulation of metavalent bonding to stabilize metastable phase: A strategy for enhancing zT in GeSe

AbstractExploration of metastable phases holds profound implications for functional materials. Herein, we engineer the metastable phase to enhance the thermoelectric performance of germanium selenide (GeSe) through tailoring the chemical bonding mechanism. Initially, AgInTe2 alloying fosters a transition from stable orthorhombic to metastable rhombohedral phase in GeSe by substantially promoting p‐state electron bonding to form metavalent bonding (MVB). Besides, extra Pb is employed to prevent a transition into a stable hexagonal phase at elevated temperatures by moderately enhancing the degree of MVB. The stabilization of the metastable rhombohedral phase generates an optimized bandgap, sharpened valence band edge, and stimulative band convergence compared to stable phases. This leads to decent carrier concentration, improved carrier mobility, and enhanced density‐of‐state effective mass, culminating in a superior power factor. Moreover, lattice thermal conductivity is suppressed by pronounced lattice anharmonicity, low sound velocity, and strong phonon scattering induced by multiple defects. Consequently, a maximum zT of 1.0 at 773 K is achieved in (Ge0.98Pb0.02Se)0.875(AgInTe2)0.125, resulting in a maximum energy conversion efficiency of 4.90% under the temperature difference of 500 K. This work underscores the significance of regulating MVB to stabilize metastable phases in chalcogenides.

Broadband Room-Temperature Photodetection via InBiTe3 Nanosheet.

Broadband room-temperature photodetection has become a pressing need as application requirements for communication, imaging, spectroscopy, and sensing have evolved. Topological insulators (TIs) have narrow bandgap structures with a wide absorption spectral response range, which should meet the requirements of broadband detection. However, owing to their high carrier concentration and low carrier mobility resulting in poor noise equivalent power (NEP), they are generally considered unsuitable for photodetection. Here, InBiTe3 alloy nanosheet formed by doping In2Te3 into Bi2Te3(≈ 1:1) is utilized, effectively improving carrier mobility by over ten times while maintaining a narrow bandgap structure, to fabricate a broadband photodetector covering a wide response range from visible to millimeter wave (MMW). Under the synergistic multi-mechanism of the photoelectric effect in the visible-infrared region and the electromagnetic-induced potential well (EIW) effect in Terahertz band, the performance of NEP=75pWHz-1/2 and response time τ ≈100µs in visible to infrared band and the performance of NEP=6.7×10-3pWHz-1/2, τ ≈8µs in Terahertz region are achieved. The results demonstrate the promising prospects of topological insulator alloy (like InBiTe3) nanosheet in optoelectronic detection applications and provide a direction for the research into high-performance broadband photoelectric detectors via TIs.

The mechanism of EP/SiC coating modulated DC flashover characteristics of epoxy composites in SF6/N2 mixtures

Surface flashover is an inevitable insulation issue for basin-type insulators in gas-insulated switchgears/lines, which significantly challenges the reliability of the electrical power systems. Previous studies have indicated that polymer/semiconductor-filler composite coatings effectively improve the insulation properties; however, the influence mechanism of the coating materials on flashover has not been demonstrated from a molecular perspective. In this work, epoxy/silicon-carbide (EP/SiC) composites were coated onto an EP substrate. The energy-level structure, surface trap, surface charging, and DC flashover voltage in SF6/N2 were calculated and characterized, and the process by which the tailored molecular energy level influences surface charge transport and flashover characteristics was elucidated. The incorporating of SiC particles reduced the width of the bandgap and introduced shallow traps, which improved carrier mobility and surface conductivity. Quantitative analysis of charge transport indicated that the improved carrier mobility and reduced surface trap level accelerated the surface charge dissipation. This reduced the tangential electrical field distortion and surface charge density and further impeded gas ionization. When the SiC concentration was 15 wt%, the flashover performance improved by 20.88%. This study describes the mechanism by which the EP/SiC coating regulates the surface charge distribution to improve the surface flashover performance by establishing a relationship among the microscopic molecular energy-level structures, mesoscopic charge transport, and macroscopic discharge phenomena.

Adjustable anion and cation vacancies CoSe catalysts on improving activity in photoelectrochemistry and electrocatalysis

Vacancies have a significant impact on catalysts as crystal structure, band structure and surface active sites. The effect of anion and cation vacancies on the catalytic performance of CoSe was studied. Catalysts with cation Co vacancies, anion Se vacancies and anion cation double vacancies were obtained. The results show that the single Co vacancy CovSe will form many pores as the active sites in the lattice and the position of the conduction band greatly moves from 0.55 eV of CoSe to −0.46 eV. This significantly improves the electrocatalytic hydrogen evolution performance, with overpotential of 161 mV and Tafel slope of 58 mV/dec. As a comparison, the overpotential of CoSe is 401 mV (Tafel slope of 171 mV/dec). In addition, Co vacancies can also improve carrier mobility and separation efficiency, demonstrating excellent photocurrent of 11.82 mA/cm2 at 1.23 eV (RHE), with 5.91 % conversion efficiency. The overall performance of CoSev with individual Se anion vacancies is not as good as CovSe. This indicates that cationic vacancies have a greater impact on the catalyst. There was no significant improvement in the performance of the sample with double vacancies of anions and cations, indicating that the two vacancies may have offset each other.