Carrier Mobility Research Articles

Tailoring the Electron and Phonon Transport in Metavalently Bonded GeTe by Stepwise Doping

AbstractThe intertwining between thermal and electrical transport poses significant challenges to enhancing thermoelectric performance. Chemical doping with a single element often can optimize one of the parameters yet may deteriorate others, restricting the upper limit of ZT achievable. Multi‐element doping can address this interdependence, allowing for simultaneous optimization of electrical and thermal properties. However, a clear selection rule for multiple dopants remains unclear. Here, a stepwise strategy is shown to improve the thermoelectric performance of metavalently bonded GeTe by enhancing density‐of‐states effective mass, increasing carrier mobility, and reducing thermal conductivity. These effects are realized by continuously introducing band convergence, lattice plainification, and structural defects. Specifically, band convergence is achieved by Cd doping to reduce the energy offset between light and heavy bands. The lattice plainification is enabled by filling Ge vacancies with Cu, which improves carrier mobility. Lastly, the lattice thermal conductivity is reduced via increasing phonon scattering by point defects caused by Pb doping and nanoprecipitates associated with all these dopants. Consequently, a peak ZT of 2.2 at 773 K and an average ZTave of 1.27 within 300–773 K are realized in Ge0.86Pb0.1Cd0.04Te‐2%Cu2Te. This work provides a synergistic strategy to modulate electron and phonon transport in metavalently bonded materials.

PM6/L8‐BO Thin Films through Layer‐by‐Layer Engineering: Formation Mechanism, Energetic Disorder, and Carrier Mobility

ABSTRACTLayer‐by‐layer (LBL) process has emerged as a promising method in the advancement of organic photovoltaics, emphasizing scalability and reproducibility. More importantly, it provides enhanced morphological control for boosting carrier mobility (μ) and power conversion efficiency. By employing a multiscale approach that combined first‐principles calculations, molecular dynamics simulations, and kinetic Monte Carlo methods, the relationship between LBL morphology engineering and carrier mobility in donor/acceptor (PM6/L8‐BO) thin films is elucidated. During solvent evaporation, the order of solid‐phase formation in LBL films was top surface, bottom region, and then the middle region. The early solid precipitation from precursor solutions was acceptor, resulting in a well‐ordered molecular arrangement and reducing energy disorder of acceptor LUMO levels. Furthermore, the difference in energy disorders between the A/D blend region and the pure A or D domains enabled LBL morphology engineering to balance electron and hole mobilities, thereby mitigating charge accumulation and recombination. LBL‐manufactured films presented higher carrier mobility ( = = 1.9 × 10−3 cm2 V−1 s−1) compared to bulk heterojunction (BHJ) films ( > = 0.1 × 10−3 cm2·V−1 s−1). These mechanisms provided insights into strategies for enhancing charge extraction of photo‐generated charge carriers through LBL engineering, driving the development of efficient organic photovoltaic materials.

Electrochemical Performance of Guanidinium Salt-Added PVP/PEO Solid Polymer Electrolyte with Superior Power Density

Solid polymer electrolytes (SPEs) for symmetrical supercapacitors are proposed herein with activated carbon as electrodes and optimized solid polymer electrolyte membranes, which serve as the separators and electrolytes. We propose the design of a low-cost solid polymer electrolyte consisting of guanidinium nitrate (GuN) and poly(ethylene oxide) (PEO) with poly(vinylpyrrolidone) (PVP). Using the solution casting approach, blended polymer electrolytes with varying GuN weight percentage ratios of PVP and PEO are prepared. On the blended polymer electrolytes, structural, morphological, vibrational, and ionic conductivity are investigated. The solid polymer electrolytes’ morphology and level of roughness are examined using an FESEM. The interlinking bond formation between the blended polymers and the GuN salt is verified by FTIR measurements, indicating that the ligands are chemically complex. We found that, up to 20 wt.% GuN, the conductivity value increased (1.84 × 10−6 S/cm) with an increase in mobile charge carriers. Notably, the optimized PVP/PEO/20 wt.% solid polymer electrolyte was fabricated into a solid-state symmetrical supercapacitor device, which delivered a potential window of 0 to 2 V, a superior energy density of 3.88 Wh kg−1, and a power density of 1132 W kg−1.

Advantages and Challenges of Graphene Transistors for High-Frequency Applications

Graphene is regarded as an ideal material for next-generation high-frequency (HF) electronic devices, attributed to its unique two-dimensional structure, high carrier mobility, and exceptional electrical properties. In recent years, the limitations of conventional silicon-based technologies for high-frequency applications have become increasingly apparent, resulting in heightened interest in graphene transistors, which exhibit significant potential for applications in wireless communications, radar systems, and terahertz technology. These transistors exhibit high cutoff frequency and low noise characteristics, along with favorable bipolar properties, which provide them with significant advantages in radio frequency (RF) applications. However, despite the significant theoretical advantages of graphene materials, their practical application is still restricted by multiple factors. Specifically, insufficient voltage gain from weak current saturation, material uniformity issues, and large-scale production challenges have restricted the widespread adoption of graphene transistors in high-frequency electronic devices. This paper reviews the relevant literature, examines the disparity between the electrical performance and practical applications of graphene transistors, and identifies the key factors influencing their implementation. The results demonstrate that targeted bandgap engineering, innovative device architectures, and the exploration of new materials can help graphene transistors can mitigate existing challenges and position themselves as key components in future HF electronic devices, driving significant advancements and broader integration of related technologies.

Research on Application of diamond MOSFET in DCDC converter

This paper focuses on the industrial application of diamond power devices and DCDC converters, carries out the application research of diamond MOSFET in DCDC converters, analyzes the limitations of current silicon-based DCDC converters and how diamond MOSFET should make up for this limitation. This paper summarizes the research on the practical application of diamond power devices at home and abroad and points out that there is a gap in the application of diamond MOSFETs in DCDC converters. Diamond has the advantages of a large band gap, high carrier mobility, high temperature and high pressure resistance, so the application of diamond MOSFET in a DCDC converter can improve its operating frequency, input and output voltage and efficiency. This paper also discusses the difficulties encountered by diamond semiconductor materials and diamond power devices in the research and industrial fields, as well as the research status of diamond semiconductor materials at home and abroad, and gives the research method for the future application of diamond MOSFET in DCDC converters. The study can use the analogy of applying SiC or GaN to DCDC converters improving their performance, and redesigning the drive circuit to match the limiting performance of diamond power devices. By applying diamond MOSFET into the DCDC converter, its operating voltage, operating frequency, output power and efficiency will be greatly improved.

Eu-Substituents-Induced Modifications in the Thermoelectric Properties of the Zintl Phase Ba1-xEuxZn2Sb2 System

Four quaternary Zintl phase thermoelectric (TE) materials belonging to the Ba1-xEuxZn2Sb2 (x = 0.02(1), 0.04(1), 0.08(1), 0.15(1)) system were successfully synthesized using the molten Pb-flux or the conventional high-temperature reaction methods. Their crystal structures were characterized by both powder and single-crystal X-ray diffraction analyses, and all four isotypic title compounds adopted the orthorhombic BaCu2S2-type (Pnma, Z = 4, Pearson code oP20) structure. The radius ratio criterion, based on the cationic and anionic elements (i.e., r+/r−), was successfully verified in the title system, as in our previous reports, where r+/r− > 1 for the BaCu2S2-type structure. A series of density functional theory calculations were performed using a hypothetical model with the idealized compositions of Ba0.75Eu0.25Zn2Sb2, and the results were compared with the ternary parental compound BaZn2Sb2 to understand the influence of Eu substituents in the Ba1-xEuxZn2Sb2 system. A similar overall shape of the density of states (DOS) curves and the near-constant DOS values at EF before and after the cationic substitution suggest only marginal changes in the carrier concentration. Therefore, carrier mobility has a dominant role in rationalizing the observed variations in the electrical transport properties of the title system. Temperature-dependent TE property measurements proved that an increase in the Seebeck coefficient S and a decrease in electrical conductivity σ were observed as the Eu substituents gradually increased in the Ba1-xEuxZn2Sb2 system, although the overall S and σ values were lower than those in the parental compound BaZn2Sb2. The thermal conductivities of these title compounds were successfully lowered by phonon scattering, but due to the overall smaller electrical transport properties, the observed maximum ZT was 0.49 at 773 K for Ba0.98(1)Eu0.02Zn2Sb2.

Study of temperature dependences and electrical properties of thin films of Ag2S quantum dots

The results of studying the electrical properties of thin films of colloidal quantum dots (QDs), Ag2S/SiO2 and Ag2S/SiO2/Au, are interesting and important for understanding the behavior of these materials. Additional studies made it possible to determine the temperature dependences of conductivity in the range from 300 to 360 K, which made it possible to study changes in the electrical properties of materials depending on temperature. Activation energy values obtained from linear approximations of current-voltage characteristics in Arrhenius coordinates have become key to determining energy barriers and conduction mechanisms in these systems. Decorating Ag2S quantum dots with plasmonic gold nanoparticles also has the potential to improve the electrical properties of materials and create new functional characteristics. The results obtained can have a wide range of applications in the field of nanoelectronics, optoelectronics, sensors and other technologies that require precise control of the electrical properties of materials at different temperatures. Decoration of Ag2S/SiO2 QDs with plasmonic gold nanoparticles leads to an increase in the band gap from 0.29 to 0.89 eV. This effect can be explained by the interaction between gold plasmons and Ag2S/SiO2 electrons, which leads to a change in the properties of the material. It has been shown that decorating Ag2S/SiO2 QDs with Au nanoparticles leads to a change in the type of conductivity. Finally, calculating the mobility of charge carriers according to the Mott-Gurney model allows for a deeper understanding of the conductivity mechanisms in the presented thin-film structures.

Enhanced carrier mobility in strain-engineered PdAs2 monolayer boosted by suppressing interband scattering.

Strain engineering is an effective method to modulate the electronic properties of two-dimensional materials. In this study, we theoretically studied the carrier mobility of the PdAs2 monolayer under different biaxial tensile strains based on the state-of-the-art electron-phonon coupling theory. We observe that the carrier mobility is largely enhanced for both n-type and p-type PdAs2 monolayers. The electron mobility experiences a rapid increase under tensile strain over 2% and can reach 670 cm2 V-1 s-1 under 4% strain, which is higher than common 2D semiconductors. The rapid increase of electron mobility originates from the ordering change of the conduction bands and the suppressed interband scattering. Our study highlights the role of electron-phonon coupling in the electron transport and provides new insights into the optimization of carrier mobility.

Boosting thermoelectric properties of n-type PbS across a broad temperature range through doping with trace amounts of InBi

Lead sulfide (PbS) is a promising thermoelectric material due to its high availability, thermal stability, and cost-efficiency, with research predominantly aiming to enhance its carrier concentration through heavy doping for optimal ZT values at high temperatures. However, this approach often results in suboptimal performance at ambient temperature, significantly constraining its applicability in thermoelectric cooling technologies. In this work, the carrier concentration of n-type PbS is optimized by incorporating trace amounts of InBi. Due to the low carrier concentration, PbS retains a high Seebeck coefficient and carrier mobility, resulting in a high average power factor (PFave) of 15.4 μW·cm−1·K−2 within the temperature range from 300 to 773 K. In addition, the introduction of In/Bi interstitial atoms and dislocation defects enhances phonon scattering, effectively reducing the lattice thermal conductivity of PbS. The peak ZT value of Pb0.999(InBi)0.001S at 773 K reaches ∼1.0, while an average ZT value (ZTave) of ∼0.6 is achieved between 300 and 773 K in Pb0.9995(InBi)0.0005S. This study demonstrates that trace element doping is an effective strategy for optimizing the thermoelectric performance of PbS across a wide temperature range, which is vital in the thermoelectric power generation and refrigeration application.

Manipulation of field-effect transistors by flexoelectric effect

Flexoelectric field-effect transistors (FE-FETs) hold significant potential for applications in biomedical and healthcare sensing fields. While existing piezoelectric FETs sense physiological signals based on pressure or compressive strain, movements such as bending of the elbow or knee joints are more common in physiological activities than external pressure. To address this, this study innovatively introduces FE-FETs that are regulated through the flexoelectric effect induced by bending. In this study, MoS2 with flexoelectric properties is utilized as the channel region. By bending the FE-FETs, the flexoelectric effect is induced, generating a flexoelectric response voltage that alters the Schottky barrier. The results confirm that varying the bending angle of the FE-FETs effectively modulates their transconductance and carrier mobility. Remarkably, the combination of traditional gate voltage and the flexoelectric effect results in a maximum carrier mobility of 49.63 cm2/V · s within a drain voltage range of 0–1 V, which is approximately 10.6 times higher than the carrier mobility of 4.68 cm2/V·s under traditional gate voltage alone. This study provides an effective approach to regulating FE-FETs and expands the possibilities for their application in wearable technology.

First-principles study on electronic and optical properties of perovskite light-emitting diodes CsPb(Br1− xIx)3

CsPb(Br1−xIx)3, a mixed-halide all-inorganic perovskite, is a promising light-emitting diode (LED) material due to its impressive performance. It has been demonstrated that the mixing parameter x of halogen composition significantly influences the luminescence efficiency of CsPb(Br1−xIx)3. However, the underlying microscopic mechanisms remain unclear. Using first-principles calculations, we investigate the effects of anion mixing on the radiative and non-radiative recombination properties of perovskite materials. Simulations on the carrier mobility, exciton binding energy, affinity energy, and defect formation energy of the materials in the CsPb(Br1−xIx)3 system collaboratively revealed that a high ratio off Br is associated with enhanced luminescence efficiency. Specifically, CsPb(Br1−xIx)3 exhibits optimal luminescent performance with a 2:1 bromine-to-iodine ratio, while it shows the performance degradation with a 1:1 ratio. The results demonstrate that the ratio of halogen atoms (Br and I) has a significant influence on the LED properties of cesium-based all-inorganic perovskites CsPb(Br1−xIx)3, providing a valuable guide for the experimental preparation of cesium-based all-inorganic perovskites.

Raman activity and high electron mobility of piezoelectric semiconductor GaSiX2 (X = N, P, and As) toward flexible nanoelectronic devices

Abstract Inspired by the urgent demand for novel multifunctional materials in advanced technology applications, herein, first-principles calculations are utilized to construct new two-dimensional GaSiX 2 (X = N, P, As) monolayers. After optimizing the GaSiX 2 crystal structures, their stabilities, Raman responses, piezoelectricity, and electronic/transport characteristics are systematically studied. Results from phonon dispersions, ab initio molecular dynamics simulations, elastic constants, and cohesive energies confirm the good dynamic, thermal, energetic, and mechanical stabilities of the proposed GaSiX 2 monolayers. Based on the Heyd–Scuseria–Ernzerhof approach, the GaSiX 2 exhibit semiconductor behaviors with favorable bandgaps for absorption of the visible spectrum of 1.82 for GaSiP2 and 1.43 eV for GaSiAs2 monolayer. In addition, the GaSiX 2 monolayers also show piezoelectric effects, and high in-plane piezoelectric coefficients d 11 are found for the GaSiP2 (−1.16 pm V − 1 ) and GaSiAs2 (−1.26 pm V − 1 ). The carrier mobilities of the GaSiX 2 are estimated by the deformation potential method for their transport properties. Along two in-plane transport directions, the carrier mobilities of the GaSiX 2 are anisotropy for holes and electrons. GaSiP2 and GaSiAs2 show large electron mobilities along the x axis of 2816.99 and 1211.41 cm2V−1s−1, respectively. Thus, the GaSiP2 and GaSiAs2 monolayers not only have high anisotropic electron mobilities but also favorable bandgaps and large piezoelectric coefficients, indicating potential applications of GaSiP2 and GaSiAs2 in electronic, photovoltaic, and piezoelectric devices. The findings of this study may provide insights into the GaSiX 2 monolayers for multifunctional applications.

Anion Transport by Bambusuril-Bile Acid Conjugates: Drastic Effect of the Cholesterol Content.

Artificial anion transporters offer a potential way to treat deficiencies in cellular anion transport of genetic origins. In contrast to the large variety of mobile anion carriers and self-assembled anion channels reported, unimolecular anion channels are less investigated. Herein, we present a unique example of a unimolecular anion channel based on a bambusuril (BU) macrocycle, a well-established anion receptor. The BU structure was expanded by appending various bile acid residues allowing a single molecule to span the membrane. Chloride transport mediated by BUs through lipid bilayers was investigated in liposomes and these studies revealed a surprisingly high dependence of the anion transport activity on the cholesterol content in the liposomal membrane.

Stereoactive Lone-Pair Manipulation for High Thermoelectric Performance of GeSe-Based Compounds.

Materials with high crystallographic symmetry are supposed to be good thermoelectrics because they have high valley degeneracy (NV) and superb carrier mobility (μ). Binary GeSe crystallizes in a low-symmetry orthorhombic structure accompanying the stereoactive 4s lone pairs of Ge. Herein, we rationally modify GeSe into a high-symmetry rhombohedral structure by alloying with GeTe based on the valence-shell electron-pair repulsion theory. We demonstrate that the substitution of Se by Te weakens the stereoactivity of the Ge lone-pair electrons, resulting in robust rhombohedral structures of GeSe1-xTex for x ≥ 0.3 at room temperature. The increase of crystal symmetry not only boosts NV from 2 for orthorhombic GeSe to 9 for rhombohedral GeSe1-xTex but greatly enhances μ from <5 to >10 cm2 V-1 s-1 (room-temperature values), thereby remarkably elevating the power factors by 2 orders of magnitude (26.9 μW cm-1 K-2 at 638 K for x = 0.5). Surprisingly, despite their higher crystallographic symmetry, rhombohedral GeSe1-xTex compounds display even lower lattice thermal conductivities (∼1.0 W m-1 K-1 at 300 K for x = 0.5) than binary GeSe (∼2.5 W m-1 K-1 at 300 K) due to abundant alloying defects in the Se-Te sublattice and ferroelectric instability. Altogether, a maximum ZT value of ∼1.1 at 638 K is achieved in rhombohedral GeSe0.5Te0.5, which already outperforms GeTe. This work provides an avenue for engineering the thermoelectric properties of low-symmetry compounds containing lone-pair electrons.

High Mobility Emissive Organic Semiconductors for Optoelectronic Devices.

High mobility emissive organic semiconductors (HMEOSCs) are a kind of unique semiconducting material that simultaneously integrates high charge carrier mobility and strong emission features, which are not only crucial for overcoming the performance bottlenecks of current organic optoelectronic devices but also important for constructing high-density integrated devices/circuits for potential smart display technologies and electrically pumped organic lasers. However, the development of HMEOSCs is facing great challenges due to the mutually exclusive requirements of molecular structures and packing modes between high charge carrier mobility and strong solid-state emission. Encouragingly, considerable advances on HMEOSCs have been made with continuous efforts, and the successful integration of these two properties within individual organic semiconductors currently presents a promising research direction in organic electronics. Representative progress, including the molecular design of HMEOSCs, and the exploration of their applications in photoelectric conversion devices and electroluminescent devices, especially organic photovoltaic cells, organic light-emitting diodes, and organic light-emitting transistors, are summarized in a timely manner. The current challenges of developing HMEOSCs and their potential applications in other related devices including electrically pumped organic lasers, spin organic light-emitting transistors are also discussed. We hope that this perspective will boost the rapid development of HMEOSCs with a new mechanism understanding and their wide applications in different fields entering a new stage.

Improving the Thermal Stability of Indium Oxide n-Type Field-Effect Transistors by Enhancing Crystallinity through Ultrahigh-Temperature Rapid Thermal Annealing.

Ultrathin indium oxide films show great potential as channel materials of complementary metal oxide semiconductor back-end-of-line transistors due to their high carrier mobility, smooth surface, and low leakage current. However, it has severe thermal stability problems (unstable and negative threshold voltage shifts at high temperatures). In this paper, we clarified how the improved crystallinity of indium oxide by using ultrahigh-temperature rapid thermal O2 annealing could reduce donor-like defects and suppress thermal-induced defects, drastically enhancing thermal stability. Not only does more crystalline indium oxide depict the high stability of threshold voltage in stringent high-temperature test environments and under positive bias, but it also shows much less degradation under forming gas annealing than as-deposited transistors. Furthermore, we also successfully solved the channel length-dependent threshold voltage problem, which is often observed in oxide transistors, by suppressing defects induced by the metal deposition process and metal doping.

Direct Evidence of Excessive Charge-Carrier-Induced Degradation in InP Quantum-Dot Light-Emitting Diodes.

The limited operational lifetime of quantum-dot light-emitting diodes (QLEDs) poses a critical obstacle that must be addressed before their practical application. Specifically, cadmium-free InP-based QLEDs, which are environmentally benign, experience significant operational degradation due to challenges in charge-carrier confinement stemming from the composition of InP quantum dots (QDs). This study investigates the operational degradation of InP QLEDs and provides direct evidence of the degradation process. To facilitate degradation studies, a double-emission structure was designed. We employed transient electroluminescence and photoluminescence for nondestructive analysis of charge-carrier dynamics during device degradation. The time-resolved emission sequence revealed changes in carrier mobility within the QD layer as devices degraded. Furthermore, prolonged exposure of QDs to the charge-carrier population hindered their radiative recombination. Our observations indicate clear evidence of QLED degradation, characterized by ligand detachment from the QD surface and deterioration of the hole-transporting material due to excessive electrons. This comprehensive analysis of degradation mechanisms in InP QLEDs lays the groundwork for improving operational stability and longevity, serving as a benchmark for future research and development in the field of nanocrystal-based electroluminescent devices.

Uncovering the Performance Enhancing Mechanism of Methanesulfonate Ligands in Perovskite Quantum Dots for Light-Emitting Devices.

Perovskite quantum dots (PQDs) have attracted more and more attention in light-emitting diode (LED) devices due to their outstanding photoelectric properties. Surface ligands not only enable size control of quantum dots but also enhance their optoelectronic performance. However, the efficiency of exciton recombination in PQDs is often hindered by the desorption dynamics of surface ligands, leading to suboptimal electrical performance. In this study, sodium methanesulfonate (NaMeS) was successfully introduced during PQD synthesis and ligand exchange, where the S═O groups effectively interacted with the perovskite components. The NaMeS-modified PQD films exhibited significantly improved surface morphology, radiative recombination efficiency, and carrier mobility. Consequently, Pe-LEDs derived from NaMeS-capped PQDs achieved a remarkable enhancement in performance with a maximum external quantum efficiency of 9.41%. This work thus provides a novel and effective strategy for the development of high-performance PQDs and their applications in LEDs.

An Amorphous Donor-Acceptor Conjugated Polymer with Both High Charge Carrier Mobility and Luminescence Quantum Efficiency.

Organic semiconducting polymers play a pivotal role in the development of field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs), owing to their cost-effectiveness, structural versatility, and solution processability. However, achieving polymers with both high charge carrier mobility (μ) and photoluminescence (PL) quantum yield (Φ) remains a challenge. In this work, we present the design and synthesis of a novel donor-acceptor π-conjugated polymer, TTIF-BT, featuring a di-Thioeno[3,2-b] ThioenoIndeno[1,2-b] Fluorene (TTIF) backbone as the donor component. TTIF-BT exhibits comparable hole mobility and enhanced interchain-mediated emissions compared to state-of-the-art semiconducting IDT-BT, leading to a remarkable Φ·μ value of ~0.084 cm2 V-1 s-1. Through time-resolved absorption and PL techniques, we propose a model to extract the spectral weight of interchain-mediated emissions, yielding 62% in TTIF-BT. Our results introduce a high-performance semiconducting polymer, which has potential use in next-generation organic optoelectronic devices, including electrically-driven polymer lasers and active-matrix display technologies.

An Amorphous Donor‐Acceptor Conjugated Polymer with Both High Charge Carrier Mobility and Luminescence Quantum Efficiency

An Amorphous Donor‐Acceptor Conjugated Polymer with Both High Charge Carrier Mobility and Luminescence Quantum Efficiency