High Carrier Mobility Research Articles

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.

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.

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.

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.

Linkage Regulation of β-Ketoamine Covalent Organic Frameworks for Boosting Photocatalytic Overall Water Splitting.

Two dimensional β-ketoamine covalent organic frameworks (2D TP-COFs) are one category of promising metal-free catalysts for photocatalytic overall water splitting (OWS) because of their unusual stability and versatile electronic/optical properties. However, none of the currently reported TP-COFs can accomplish the hydrogen evolution (HER) and oxygen evolution reactions (OER) simultaneously without adding any sacrificial agents and cocatalysts. To address this challenging issue, we rationally designed 23 2D TP-COFs by regulating the linkage groups and comprehensively evaluated their OWS activity by using the first-principles method. First, the electronic band structure calculations at the HSE06 level reveal that the band gap can be reasonably adjusted with values ranging from 1.67-3.16 eV. Among these 23 systems, 10 TP-COFs are realized to match well with both the chemical potentials of H2/H+ and O2/H2O, which are capable of visible-light-driven OWS from an electronic perspective. Further thermal activity results on OWS demonstrate that only Hep-BDA (heptazine-aniline) and Bpy-4 (bipyrimidinamine) based COFs can satisfy the completely spontaneous of HER and OER under light irradiation and neutral conditions. Importantly, the calculated small exciton binding energies and high carrier mobility for Hep-BDA and Bpy-4 TP-COFs propose they are potentially applied in photocatalytic OWS. We also achieved the theoretical energy conversion efficiency of Hep-BDA can reach as high as 13.01%. Because there are very few successful applications of TP-COFs on OWS, this theoretical work not only offers valuable insights and innovative ideas for the exploration of novel metal-free photocatalysts for OWS but also supplies a direction for the development of new TP-COF derivatives.

First-principles study of a novel type-II As2C3/MoSi2N4 heterostructure with high carrier mobility in photocatalytic water splitting

First-principles study of a novel type-II As2C3/MoSi2N4 heterostructure with high carrier mobility in photocatalytic water splitting

High-performance broad-spectrum self-powering photoelectrochemical photodetectors based on MnPSe3 nanosheets

Transition metal phosphorus trichalcogenides (MPX3), as a group of layered van der Waals materials with wide tunable bandgaps, high carrier mobility and good light absorption, are potential candidates for the preparation of high-performance broad-spectrum photoelectrochemical photodetectors (PEC PDs). MnPSe3, a p-type semiconducting material in the MPX3 family, was exfoliated into nanosheets using liquid-phase exfoliation, and then applied in the PEC PDs. The MnPSe3-based PEC PDs were thoroughly investigated in a three-electrode system and demonstrated self-powered photoelectric performance across a broad spectral range of 400-800nm. Specifically, under 400nm illumination, the photodetector showed the optimal performance with a photocurrent density of 9.72 μA/cm2, responsivity of 85.55 μA/W, response times of 10/15 ms and fine cyclic stability under the biased condition. In addition, effects of different stripping agents, bias voltages, wavelengths and optical powers on the device performance were compared. These findings suggest that MnPSe3 is a highly promising material in applications of high-performance self-powered PEC PDs.

Application of Advanced Quantum Dots in Perovskite Solar Cells: Synthesis, Characterization, Mechanism, and Performance Enhancement

Quantum dots have garnered significant interest in perovskite solar cells (PSCs) due to their stable chemical properties, high carrier mobility, and unique features such as multiple exciton generation and far-fetched...

A new carbon allotrope with high carrier mobility and optical absorption.

Carbon atom has different bonding modes, which provides the possibility for the existence of multilayer carbon allotropes. Among these bonding modes, the sp3 hybrid bonding mode often causes atoms to be noncoplanar. This provides the possibility for the emergence of two-dimensional (2D) multilayer materials. In this work, a new 2D multilayer carbon allotrope named trilaminar buckled T-graphene is proposed. Carbon atoms have sp2 and sp3 hybridization in this structure. It is nonmagnetic and has an indirect band gap of 1.70 eV. It has mechanical stability and dynamic stability, and formation energy calculations also prove that it is stable. Thermal stability calculations results indicate that it does not change the bonding pattern at 1000 K. It is an elastically soft material with a low value of elastic constants. This structure shows amazing electrical properties, which has a high hole mobility of close to 3071 cm2 V-1 s-1. Optical property calculations results show that it has an optical gap of 1.70 eV and an ultrahigh absorption in visible and near ultraviolet light. Considering all its properties, this structure has great application potential in high-speed electronic and optoelectronic devices, optical filters, modified substrates, and adsorption sensors.

First-principles investigation of the photocatalytic properties of two-dimensional CdO/ZrSSe heterojunctions.

Two-dimensional van der Waals heterojunction materials have demonstrated significant potential for photocatalytic water splitting in hydrogen production, owing to their distinct electronic and optical properties. Among these materials, direct Z-scheme heterojunctions have attracted considerable attention in recent research. In this study, a novel CdO/ZrSSe heterojunction is designed using first-principles calculations. The structural stability, electronic properties, carrier mobility, optical absorption, and photocatalytic performance of this heterojunction are systematically investigated, with a particular focus on the influence of strain on the band structure. The results reveal that both type-I and type-II heterojunctions exhibit staggered, indirect bandgap structures, with bandgap values of 0.80 eV and 0.60 eV, respectively. A built-in electric field is established from the CdO layer to the ZrSSe layer, facilitating oxidation in the ZrSSe layer and reduction in the CdO layer. The highest carrier mobilities are calculated to be 462 cm2 V-1 s-1 and 2738 cm2 V-1 s-1, respectively. Under compressive strain, the bandgap widths of both I-CdO/ZrSSe and II-CdO/ZrSSe heterojunctions decrease, whereas tensile strain results in an increase in the bandgap width. Correspondingly, the optical absorption peaks of both heterojunctions are enhanced under compressive strain and diminished under tensile strain. These findings suggest that the performance of both type-I and type-II CdO/ZrSSe heterojunctions surpasses that of their individual monolayers, exhibiting a typical Z-scheme photocatalytic mechanism, and thus positioning them as promising high-efficiency catalysts for water splitting.

Recent progress in two-dimensional Bi2O2Se and its heterostructures.

Ever since the identification of graphene, research on two-dimensional (2D) materials has garnered significant attention. As a typical layered bismuth oxyselenide, Bi2O2Se has attracted growing interest not only due to its conventional thermoelectricity but also because of the excellent optoelectronic properties found in the 2D limit. Moreover, 2D Bi2O2Se exhibits remarkable properties, including high carrier mobility, air stability, tunable band gap, unique defect characteristics, and favorable mechanical properties. These properties make it a promising candidate for next-generation electronic and optoelectronic devices, such as logic devices, photodetectors, sensors, energy technologies, and memory devices. However, despite significant progress, there are still challenges that must be addressed for widespread commercial use. This review provides an overview of progress in Bi2O2Se research. We start by introducing the crystal structure and physical properties of Bi2O2Se and a compilation of methods for modulating its physical properties is further outlined. Then, a series of methods for synthesizing high-quality 2D Bi2O2Se are summarized and compared. We next focus on the advancements made in the practical applications of Bi2O2Se in the fields of field-effect transistors (FETs), photodetectors, neuromorphic computing and optoelectronic synapses. As heterostructures induce a new degree of freedom to modulate the properties and broaden applications, we especially discuss the heterostructures and corresponding applications of Bi2O2Se integrated with 0D, 1D and 2D materials, providing insights into constructing heterojunctions and enhancing device performance. Finally, the development prospects for Bi2O2Se and future challenges are discussed.

Enhancing the electronic and photocatalytic properties of (SnO2)n/(TiO2)m oxide superlattices for efficient hydrogen production: a first-principles study.

The effects of biaxial tensile and compressive strain on the structural, electronic, and photocatalytic properties of tetragonal [001] (SnO2)n/(TiO2)m superlattices have been theoretically explored using density functional theory (DFT) calculations. Various stacking periodicities between n SnO2 layers and m TiO2 layers, including (n = m), (n, 1), and (1, m) were studied in the context of water splitting for hydrogen production. The results reveal that the (1, m) stacking periodicity exhibit the highest bulk modulus, Poisson's ratio, and Debye temperature values. Phonon dispersion analysis showed excellent stability for the (SnO2)3/(TiO2)1 superlattice under both tensile and compressive strains ranging from -5% to 5%, while other superlattices remain stable within the range of -3% to 4%. Furthermore, the electronic analysis revealed a decreasing trend in the band gap for all structures as the tensile strain increases. A tunable band gap from 3.34 eV to 2.54 eV under tensile strains for (SnO2)1/(TiO2)3 was found using the HSE06 functional, exhibiting high carrier mobility. Favorable band edge alignments at pH 0, 7, and 14 highlight the potential of these superlattices as efficient photocatalysts. The results demonstrate that applying tensile strain to (SnO2)n/(TiO2)m superlattices with high TiO2 thickness can result in optimal band gap values and favorable band edge alignments with the water redox potentials. This makes these superlattices promising for hydrogen production from water splitting.

Charge noise in low Schottky barrier multilayer tellurium field-effect transistors.

Creating van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and high carrier mobilities for bipolar transport, which are crucial for constructing fundamental building blocks like diodes and transistors in a 2D architecture. Following the recent discovery of elemental 2D tellurium, here, we systematically investigate the electrical transport and flicker noise of hydrothermally grown multilayer tellurium field effect transistors. While the devices exhibit a dominant p-type behavior with high hole mobilities up to ∼242 cm2 V-1 s-1 at room temperature and almost linear current-voltage characteristics down to 77 K, ambipolar behavior was observed in some cases. Through a detailed temperature dependent transport characterization, we estimated the Schottky barrier height as low as ∼20 meV. The good electrical contacts further facilitate the observation of metal-to-insulator transition at low temperature, being an intrinsic property of the tellurium channel rather than the contacts. Finally, detailed low frequency noise spectroscopy shows dominant 1/f type behavior across the entire gate-voltage range. The origin of the observed noise can be described by Hooge's mobility fluctuation model, rather than the carrier number fluctuations due to interfacial traps. We anticipate that such analysis will contribute to the development of futuristic low-noise devices using tellurium.

Graphene Composite Based Flexible Sensors for Wearable Applications

mwymwAbstract:In recent years, flexible wearable sensors have received widespread attention for their potential application value in motion monitoring, healthcare and human-computer interaction. Graphene, as a two-dimensional zero-bandgap semi-metallic material, is an ideal material for the preparation of wearable flexible sensors due to its high carrier mobility, mechanical flexibility, and biocompatibility. Based on target species and performance requirements, researchers utilize graphene and its redox products to form carbon nanocomposites by combining them with polymers, metals and other substrates through specific preparation methods. This helps to increase the number of active sites and functional groups of modified graphene, achieving dispersion and functionalization of graphene. Such materials can effectively solve the current problems of low sensitivity and poor sustainability faced by pure graphene flexible sensors in the wearable field and promote the maturity of next-generation flexible electronic products in diversified directions. This review starts from the types and classic preparation methods of graphene composites. Then it elaborates the principles and applications of existing pressure/strain, biological, and humidity graphene composites based wearable flexible sensors. Finally, the paper comprehensively summaries the problems and challenges at the present stage and proposes the future development trends.

Synthesis and Characterization of Functionalized Poly(9-vinylcarbazole) for light-emitting diode applications

Organic light-emitting diode (OLED) has been successfully applied to replace conventional lighting systems due to its ability to adjust color emission, low energy consumption, and high contrast ratio. One of the polymers of interest in this area is polyvinyl carbazole, PVK, given its characteristics, such as forming stable radicals, high thermal and photochemical stability, and high charge carrier mobility. The modification of PVK has contributed positively to its performance as an electroluminescent layer in the constitution of OLED devices, as seen in works carried out by Mota & Marques (2019); Brito & Marques (2020); Correia & Marques (2022); Geffroy & Grana (2019); Pachariyangkun & Suda (2020). The present study aimed to synthesize and functionalize poly(9-vinylcarbazole) as well as its characterization by thermoanalytical (TG, DTA and DSC) and spectroscopic (FTIR) techniques in order to verify the efficiency of the proposed synthesis. To date, no studies have been found in the literature using the compound 3-(4,4,5,5-Tetramethyl-[1,3,2]dioxaborolan-2-yl)-dibenzofuran in PVK for application in the emitting layer of optoelectronic devices.

Introducing Noncovalent Interactions in Conjugated Polymers to Enhance Backbone Coplanarity and Aggregation at the Interface to Improve Carrier Mobility.

In organic field-effect transistors (OFETs), the high carrier mobility of conjugated polymers (CPs) is significantly influenced by the maintenance of excellent coplanarity and aggregation, especially at the interface between the organic semiconductor and dielectric layer. Unfortunately, CPs typically exhibit poor coplanarity due to the single bond rotations between donor and acceptor units. Furthermore, there is relatively little research on the coplanarity of CPs at the interface. Herein, we propose a strategy of introducing noncovalent interactions to enhance the coplanarity of the backbone and promote the aggregation of the polymer at the interface, which should lead to significant enhancements in carrier mobility. The idea is proved by incorporating different volume fractions of oleic acid (OA) into poly(indacenodithiophene-co-benzothiadiazole) (IDTBT). OA can form hydrogen bonds, which has been verified by Fourier transform infrared spectroscopy (FT-IR). OA promotes the migration of IDTBT toward the interface, thereby enhancing aggregation, as verified by film-depth-dependent light absorption spectroscopy (FLAS) and contact angle (CA) experiments. The results from film-depth-dependent Raman spectroscopy (FRS), two-dimensional grazing incidence wide-angle X-ray scattering (2D GIWAXS), atomic force microscopy (AFM), and density functional theory (DFT) calculations suggest that films treated with OA exhibit enhanced backbone coplanarity and aggregation at the interface, resulting in an increase in carrier mobility to 4.24 ± 0.11 cm2 V-1 s-1 with the addition of OA.

Equal-Bilayer MoSe2 Grown by a Nucleation-Etching Strategy with High Carrier Mobility.

Bilayer transition metal chalcogenides (TMDs) have gradually attracted a great deal of attention due to the higher density of states and carrier mobility than monolayer TMDs. Controlling the uniformity of the layer number is very crucial because it will intensively influence the physical properties. However, it is difficult to synthesize equal-bilayer (EB) TMDs with two identical layers via a normal layer-by-layer strategy. Most reported bilayer TMDs are not uniform and such unequal bilayers would introduce a sizable Schottky barrier, resulting in the low carrier mobility. Here, a nucleation-etching strategy is proposed to grow EB-MoSe2 by chemical vapor deposition (CVD), which breaks the limitations of normal layer-by-layer strategy. The second layer is preferentially formed beneath the first layer rather than above, and a different etching phenomenon is also observed, which occurs more preferentially at the overlapping grain boundary sites on the top layer. The obtained EB-MoSe2 flakes are 3R-stack with high crystal quality. Furthermore, the contact between EB-MoSe2 and metal electrodes is greatly improved, thereby EB-MoSe2 transistors exhibit an order of magnitude higher carrier mobility (104 cm2 V-1 s-1) than that of UEB-MoSe2 transistors (12 cm2 V-1 s-1). This value is also at a relatively high level compared with reported results. Our work offers a feasible strategy for the synthesis of EB-TMDs with high carrier mobility, which is meaningful for developing high-performance 2D optoelectronic devices.

Halide Perovskite Photodiode Integrated CMOS Imager.

Thin film photodiodes (TFPD) can supplement complementary metal-oxide-semiconductor (CMOS) image sensor vision by their exotic optoelectronic properties assisted by their monolithic processability. Halide perovskites are known to show outstanding optoelectronic properties, such as large absorption coefficient, long carrier diffusion lengths, and high carrier mobility, leading to high external quantum efficiency (EQE) and fast charge transport in photodiodes (PDs), especially compared with other thin-film photodiode candidates. In this paper, high-resolution two-dimensional (2D) and three-dimensional (3D) imaging capabilities are demonstrated using perovskite photodetection material with a silicon (Si) read-out integrated circuit (ROIC). The integration of this perovskite photodiode (PePD) on the Si ROIC provides fine resolution for 2D imaging. The fast carrier transport properties of the PePD enable depth sensing of objects using the same sensor. 3D imaging is demonstrated using the proposed top-electrode controlled indirect time-of-flight (iToF) operation supported by the fast PD switching through the top common electrode of the TFPD image sensor pixel. It is expected that the PePDs on Si ROIC could mark a significant milestone for the TFPD imaging platform with their outstanding optoelectronic performance in combination with the CMOS image sensor technology, not only for conventional 2D imaging but also by enabling extensions toward 3D sensing, promising applications in automotive, augmented reality (AR), and virtual reality (VR).