Electron Mobility Research Articles

Enhanced Thermoelectric Performance in Vacancy-Filling Heuslers due to Kondo-Like Effect.

To improve thermoelectric efficiency, various tactics have been employed with considerable success to decouple intertwined material attributes. However, the integration of magnetism, derived from the unique spin characteristic that other methods cannot replicate, has been comparatively underexplored and presents an ongoing intellectual challenge. A previous research has shown that vacancy-filling Heuslers offer a highly adaptable framework for modulating thermoelectric properties. Here, it is demonstrated how intrinsic magnetic-electrical-thermal coupling can enhance the thermoelectric performance of vacancy-filling Heusler alloys. The materials, Nb0.75Ti0.25FeCrxSb with 0 ≤ x ≤ 0.1, feature a fraction of magnetic Cr ions that randomly occupy the vacancy sites of the Nb0.75Ti0.25FeSb half-Heusler matrix. These alloys achieve a remarkable thermoelectric figure of merit (zT) of 1.21 at 973 K, owing to increased Seebeck coefficient and decreased thermal conductivity. The mechanism is primarily due to the introduction of magnetism, which increases the density-of-states effective mass (reaching levels up to 15 times that of a free electron's mass) and simultaneously reduces the electronic thermal conductivity. Mass and strain-field fluctuations further reduce the lattice thermal conductivity. Even higher zT values can potentially be achieved by carefully balancing electron mobility and effective mass. This work underscores the substantial prospects for exploiting magnetic-electrical-thermal synergies in cutting-edge thermoelectric materials.

Hf2CO2-based heterojunctions for efficient photocatalytic hydrogen production and highly responsive self-powered flexible photodetector

The heterojunctions based transition metal carbide (MXenes) provides new possibilities for achieving high-performance photodetector. The electronic, mechanical, optical, and photocatalytic properties of the Hf2CO2-based heterojunctions are calculated based on first-principles calculations, and the photocurrent (Iph) and extinction ratio (ER) are calculated based on quantum transport simulations. The Hf2CO2/Sc2CF2, Hf2CO2/Zr2CO2, and Hf2CO2/Sc2CCl2 heterojunctions are ionic semiconductors with indirect bandgap. The Hf2CO2/Sc2CF2 heterojunction exhibits high solar to hydrogen efficiency (ηSTH) of 40.14 % and applying biaxial strain can effectively modulate the ηSTH of the Hf2CO2/Zr2CO2 heterojunction. The Hf2CO2/Zr2CO2 heterojunction has low overpotentials (ηHER) of 0.19 V and exhibits high electron mobility. The photodetector based on the Hf2CO2/Zr2CO2 heterojunction exhibits high Iph, and the photodetector based on the Hf2CO2/Sc2CF2 heterojunction has large ER and sensitivity to infrared and ultraviolet polarized light. The Iph and ER are significant increase by bending the photodetector. Our research indicates the potential applications of the Hf2CO2-based heterojunctions in photocatalytic water splitting and photodetector.

Strain mediated ultra-high electron mobility in Ge-doped two-dimensional Ga2O3

Strain mediated ultra-high electron mobility in Ge-doped two-dimensional Ga2O3

Design and optimization of high electron mobility transistor with high-k dielectric material integration

We have developed and simulated a high electron mobility transistor (HEMT) operating in the 5 nm regime. This HEMT uses hafnium oxide (HfO2), a high-k dielectric material, to create an undoped region (UR) beneath the gate. While the gate and undoped regions share equal thickness, the channel length differs. This innovative undoped under the gate dielectric HEMT design mitigates the maximum electric field (V) within the channel area, leading to a significant increase in drain current. The utilization of a high-k dielectric in the HEMT structure results in a saturated Ion current that is 60% higher compared to conventional structures. Specifically, we use an AlGaN/GaN/SiC-based HEMT with an intrinsic section below the gate, using HfO2 as the high-k dielectric substantial, for applications requiring high power and high-frequency power amplifiers. Compare this advanced HEMT design to conventional HEMTs and you will see improved conductivity, a greater drain current (Id), a 54% increase in transconductance (Gm), and a lower on-resistance (Ron). Additionally, advancements in the electric field in the Y direction are seen. This HEMT structure exhibits superior performance compared to alternative materials analyzed. The integration of AlGaN/GaN materials in HEMTs opens up extensive opportunities in the realms of radio frequency very large-scale integration (VLSI) and power electronics.

The modulation of characteristics in AlGaN/GaN High electron mobility transistors (HEMTs) using multiple field plate technology

The modulation of characteristics in AlGaN/GaN High electron mobility transistors (HEMTs) using multiple field plate technology

Janus-type BN-embedded perylene diimides via a “shuffling” strategy: Regioselective functionalizable building block towards high-performance n-type organic semiconductors

Regioselevtive functionalization of perylene diimides (PDIs) at bay area often requires multistep synthesis and strenuous recrys-tallization. Direct bromination of perylene diimides only afford the 1,6 and 1,7-regioisomers. More importantly, the 1,6-dibromo regioisomers could only be separated by preparative HPLC. Herein, we report a promising strategy for constructing Janus back-bones of BN-doped perylene diimide derivatives. This Janus-type configuration results in the unique regioselective functionalization of BN-JPDIs, which yields exclusively the 1,6-regioisomers. Further investigation shows that the Janus-type configuration leads to a net dipole moment of 1.94 D and intramolecular charge transfer, which causes substantial changes on the optoelectronic properties. Moreover, the single crystal organic field-effect transistors based on BN-JPDIs exhibit electron mobilities up to 0.57 cm2 V−1 s−1, showcasing their potential as versatile building block towards high-performance n-type organic semiconductors.

Recent Advancements in the Development of Graphene‐Based Materials for Catalytic Applications

AbstractGraphene, a two‐dimensional material, presents unprecedented opportunities for catalytic applications, attributable to its unique planar structure, outstanding optical transmittance, superior electronic conductivity and mobility, extensive specific surface area, and elevated chemical stability, coupled with its tunability. In recent years, graphene‐based catalysts have garnered significant research attention and interest. This review aims to elucidate recent advancements in the synthesis of graphene‐based catalysts. It encompasses discussions on heteroatom‐doped metal‐free graphene catalysts, graphene composite catalysts (including graphene/metal and graphene/metal oxide composites), and their applications in various catalytic domains such as electrocatalysis, photocatalysis, and catalysis of organic reactions.

Regulation on reacting solvent engineering for scalable synthesis of Na3(VOPO4)2F@carbon nanotubes microsphere cathodes towards high-power and long-lifespan Na-ion batteries

Na3(VOPO4)2F (NVOPF) has emerged as a promising cathode candidate for commercial Na-ion batteries, ascribed to its elevated theoretical energy density and robust structure during the extraction/insertion of two Na+ ions. However, the intrinsic poor electronic conductivity and unscalable materials-preparation technologies make it unexpected to stand out in large-scale energy storage systems. In this study, a spray-drying process technology is implemented to synthesize Na3(VOPO4)2F@carbon nanotubes (NVOPF@CNTs) composite through the reduction of V5+ driven by methanol at room temperature, in which the shortened Na-ion transfer path and the rapid electron mobility are facilitated by the CNTs. The resulting NVOPF@CNTs electrode exhibits exceptional capabilities, including a high discharge capacity (122.1 mA h g−1 at 1 C= 120 mA h g−1), outstanding rate performance (103.1 mA h g−1 at 100 C), and an extended lifespan (71.8 % capacity retention after 6000 cycles at 20 C). Additionally, the Na3(VOPO4)2F//NaTi2(PO4)3 full battery system demonstrates impressive high-power output capabilities (93.3 mA h g−1, 20 C), versatile current switching adaptability, and robust cycling performance (75.3 % of 98.5 mA h g−1 for the initial capacity after 3000 cycles). The study underscores the potential of improving the preparation of vanadium-based phosphate materials to enhance the practical application of Na-ion batteries.

Solution process of graphene-induced ohmic contact between the metal and AlGaN/GaN for hemts application

This work demonstrates an AlGaN/GaN high electron mobility transistor (HEMT) with Cr/Graphene ohmic contacts constructed without heat treatment. The Cr/Graphene ohmic contact was fabricated using a spray-coated graphene nanoflakes solution and electron-beam-evaporated Cr. This method does not require a high-temperature annealing step in conventional Ti/Al/Ni/Au ohmic contact. It is suggested that the Cr/graphene combination acts similarly to a doped n-type semiconductor in contact with AlGaN/GaN heterostructures, enabling carrier transport to the AlGaN layer. The investigated Au/Cr/ Graphene/AlGaN/GaN HEMT device exhibits ohmic drain characteristics in the range of -4 V to 4 V of drain-source voltage with a calculated contact resistance density of 2.5 mΩcm2. Our results have important implications for the fabrication and manufacturing of AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the future.

Perovskite nanostructure anchored on reduced graphene (rGO) nanosheets as an efficient electrocatalyst for oxygen evolution reaction (OER)

Energy is the basic need of this modern era and water splitting is the best known renewable source of energy. Designing an effective, high performing and durable electrocatalyst has become a serious endeavour to enhance water-splitting efficiency. For this purpose, a hydrothermal method was used to produce a non-toxic, environmentally friendly and cost-effective rGO/ZnSnO3, a composite material to improve water oxidation. For this, various analytical approaches were used to investigate the structural, textural, compositional, thermal and morphological features of the reported materials. The electrochemical properties of the rGO/ZnSnO3 nanohybrid was also analyzed by a three-electrode setup in a 1 M potassium hydroxide (KOH) and the resulting nanohybrid exhibited exceptionally small overpotential (212 mV) at an ideal current density (j) of 10 mA/cm2. The larger electrochemical surface area (ECSA) value 506.25 cm2, minimum charge transfer resistance (Rct) 0.18 Ω and remarkable stability around 20 h revealed that the produced composite material exhibited excellent potential for OER. Further examination revealed a significantly low Tafel value (37 mV/dec), suggesting that the rGO/ZnSnO3 nanohybrid possesses improved electrocatalytic efficiency and fast reaction kinetics. The nanohybrid mentioned above (rGO/ZnSnO3) shows significant potential for electrolysis of water and other electrochemical processes attributed to its considerable surface area, various active sites, exceptional stability, rapid electron mobility, low resistivity and favourable electrical conductivity.

Aided design and molecular regulatory mechanism of non-fused ring acceptors in the framework of A-D1-D2-A molecular systems

Non-fused ring acceptors (NFRAs) have garnered significant attention due to their low cost, ease of synthesis, and high efficiency. Molecules with asymmetric structures can improve molecular stacking and effectively reduce non-radiative energy loss. So, the asymmetric A-D1-D2-A series NFRAs (DPCT-4F and DPCT-4Cl) were selected as the research objects, and four acceptors (DPCT-D1∼DPCT-D4) were designed using end-capped modification strategies. Theoretical simulations were conducted on the ground and excited state characteristics of DPCT series molecules, and the electron mobility of the dimers formed by these acceptors was calculated. It was found that the simulated energy levels, energy gaps, absorption spectra and open-circuit voltages of original molecules are consistent with the trends in the experiment, ensuring the accuracy of the calculation method. Moreover, the nearly equal bond lengths of the developed compounds and the original molecules at the corresponding positions indicate that end-capping modification strategies have little effect on the molecular bond lengths. However, the instability of C-C single bond results in an increased dihedral angle between dipyran and cyclopentadithiophene. Among these designed molecules, DPCT-D1 and DPCT-D2, modified with -CN/-NO2 functional groups, outperform the reference molecules regarding energy gap, molecular descriptors, absorption spectrum, and exciton binding energy. This demonstrates the superiority of functional group substitution strategies with strong electron-withdrawing ability. Introducing thiophene units enables DPCT-D4 molecule to achieve a higher open-circuit voltage, dipole moment and light capture ability. Additionally, all the designed molecules exhibit higher electron mobility than DPCT-4F. DPCT-D1 shows even higher mobility than the better-performing reference molecule DPCT-4Cl due to its greater electronic coupling strength and lower reorganization energy. Overall, most tailored molecules, particularly DPCT-D1, exhibit superior performance in most critical parameters compared to the reference molecules, demonstrating the design strategy's effectiveness and offering worthwhile theoretical instruction for developing high-performance acceptors.

Asymmetric Doping‐Dependent Electron Transport Mobility in InxGa1–xAs/GaAs Quantum Well Field‐Effect Transistor Structure

We analyze the asymmetric doping‐dependent electron mobility μ of GaAs/InGaAs/GaAs quantum well field‐effect transistor (QWFET) structure. We consider doping concentrations, nd1 and nd2, in the substrate and surface barriers, respectively, and study μ as a function of nd2, taking (nd1 + nd2) unchanged. An increase in nd2 decreases nd1, yielding interesting changes in the occupation of subbands. For well width W < 164 Å, μ is due to single subband occupancy (SSO). Around W = 164 Å, there occurs first SSO, then double subband occupancy (DSO), and again SSO with an increase in nd2. Near the transition of subbands, abrupt discontinuities in μ arise due to inter‐subband effects. Thus, high to low and then high values of μ are obtained, displaying almost flat‐like variations, symmetric about |nd2 − nd1| = 0. As W becomes wider, complete DSO occurs throughout the range of nd2 having reduced μ. Alternatively, keeping nd1 unchanged and by increasing nd2, μ raises due to enhanced N s , with a drop near the transition from SSO to DSO. Under SSO, μ is controlled by the ionized impurity and alloy disorder scatterings, while under DSO, the impurity scattering determines μ. Our analysis on μ can help to examine the inter‐subband effects on device characteristics of the QWFET system.

First‐Principles Study on the Effects of Different Valence Hi and VO on the Mobility, Conductivity, and Carrier Lifetime of β‐Ga2O3: Mo5+/6+

The poor conductivity of β‐Ga2O3 limits its application in optoelectronic devices. Currently, there have been advancements in investigating the impact of Mo doping on the photoelectric characteristics of β‐Ga2O3. However, there are few studies on the impact of different valence states of Mo doping and the coexistence of O vacancy and interstitial H on the electrical properties of β‐Ga2O3. In the process of preparing β‐Ga2O3, O vacancy and interstitial H inevitably exist. In response to these problems, the first‐principles GGA + U method is used to study the impact of different valence states of Mo doping and the coexistence of interstitial H and O vacancy on the electrical properties of β‐Ga2O3. The electronic structure, mobility, conductivity, and carrier lifetime of the system are calculated and analyzed. The results show that all doping systems are more stable under Ga‐rich conditions. The band gap of the Mo‐doped β‐Ga2O3 system gradually narrows, which is mainly attributed to the Burstein–Moss effect and the multiplicity reintegration effect. Mo doping effectively improves the electrical conductivity of the system. Ga47O72Mo16+H11+ system has the longest carrier lifetime; Ga47O72Mo16+H10 has the largest mobility; Ga47O72Mo15+H10 system has the highest conductivity. Therefore, Mo‐doped β‐Ga2O3 materials help to prepare new electrical performance devices.

Construction of self-supported TiO2 nanotube arrays with hybrid point defect engineering: A bifunctional anode for Li+/Na+ storage

Point defect engineering has garnered widespread application for enhancing the dynamic behavior of anode materials and improving electrochemical performance. Herein, a hybrid point defect strategy is proposed in Ti-based oxide materials to achieve N doping induced oxygen vacancies (OVs) and subsequently accelerated electron mobility and perform better diffusion kinetics. This methodology culminates in the fabrication of self-supported nanotube arrays comprising N-doped OVs-rich TiO2 (denoted as N-TNTs). Density functional theory (DFT) calculations and electrochemical characterizations validate that, hybrid point defects lead to high electron mobility and perform better diffusion kinetics, as well as higher Li+/Na+ ions adsorption energy barrier and diffusion energy barrier, which in turn improves the rate performance and cycling stability. This research provides a forward-looking and feasible strategy for the application of point defect engineering in anode materials.

Reduction of interface defects in gate-recessed GaN HEMTs by neutral beam etching

This study investigates and compares the impact of different etching techniques on the fabrication of GaN high electron mobility transistors (HEMTs) between the inductively coupled plasma reactive ion etching (ICP-RIE) and the neutral beam etching (NBE) for the gate recess. By conducting direct current analysis, it was found that devices manufactured using the NBE exhibited superior electrical performance as compared with those produced using the ICP-RIE. These enhanced electrical characteristics include a transconductance of up to 100.4 mS/mm, a threshold voltage (Vth) of −2.3 V, an on/off current ratio of 1.1 × 109, a subthreshold swing (S.S.) of 99.63 mV/dec, and a remarkably low gate leakage current. Additionally, we noted varying degrees of hysteresis in the I–V characteristics were related to process disparities possibly leading to interface defects. Multi-frequency capacitance-voltage (C–V) measurements were used to identify the interface defects at the oxide/AlGaN interface of the gate. The results revealed that devices fabricated using the NBE exhibited a lower interface defect density as compared with those fabricated using the ICP-RIE, thereby elucidating the reduced hysteresis observed in the I–V characteristics. These findings indicated the significant advantages of the NBE process in the fabrication of GaN HEMTs.

Synthesis and characterizations of zinc oxide nanorods by cost effective aqueous hydrothermal technique for solid state lighting applications

Zinc oxide (ZnO) is recognized as the most promising and often utilized semiconducting material due to its exceptional physical, chemical, optical, and relatively low-cost production features, as well as its ecologically beneficial nature. ZnO is a prominent candidate owing to its wide band gap (3.37 eV at room temperature) as well as its high exciton binding energy (60 meV) for the next generation of ultraviolet and blue optoelectronic devices. This would be achieved through the development of hybrid heterostructured LED devices with low manufacturing costs by blending gallium nitride (GaN) with zinc oxide (ZnO), which serves as the most efficient opto-electronic device. Due to its high electron mobility, high transparency in the visible wavelength spectrum, and low work function, ZnO is also a highly investigated transparent conducting oxide thin film for several applications. Besides, their incredible optical capabilities, ZnO-based optical devices, such as light-emitting diodes (LEDs) and laser diodes (LDs), have drawn a great deal of interest. This reported research work demonstrates the growth of high-density, high-aspect-ratio ZnO nanorod (NR) arrays on p-type gallium nitride substrates employing low-cost facial aqueous hydrothermal syntheses with optimised growing conditions. Additionally, a top-down chemical etching technique is adapted for fabricating zinc oxide nanotubes. High-quality ZnO nanorods with high intensity that were a few microns long were found across the GaN substrate with FESEM analysis. The chemical composition of the grown nanorods is confirmed with EDAX analysis. The wurtzite crystalline structure and c-axis orientation of the grown ZnO NR-arrays were identified in X-ray diffraction studies. A Schimadzu UV–Vis–NIR spectrophotometer was used to record the optical curve, and the energy gap was determined to be 3.24 eV by plotting the Tauc curve. The good optical quality of the harvested nanorods is ensured by the narrow near-band-edge (NBE) emission at 384 nm and defect emission peaks detected through photoluminescence analyses. Grown specimens are also subjected to Raman spectrum analyses, and the obtained results are presented.

Elucidating roles of fulleropyrrolidine-based materials as extraordinary electron transporters for boosting efficiency of perovskite photovoltaics

To achieve an ideal electron transfer layer (ETL) for perovskite solar cell (PSC), effective compounds were developed based on fullerene C60 functionalized with a pyrrolidine ring (fulleropyrrolidine), to which a cyanoethyl group, a thiophene ring, and four DNA bases were attached. Density functional theory (DFT) calculations were employed to study structural, electronic, optical, and electron mobility features of these materials. To more precisely determine the HOMO and LUMO energy levels of all samples, the NBO calculations were accomplished at PBE0-D3/6-31G(d,p) theoretical level. The LUMO levels of all ETL samples could be aligned with the conduction band of perovskite CsFAMAPbIBr via their coupling within fabricated PSCs, enabling easy electron injection from CsFAMAPbIBr to the Ag electrode. All functionalized fullerene C60–based ETLs exhibited very high electron mobilities in the range of 0.744–1.598 cm2V−1s−1 which were significantly greater than 1.461 × 10−5 cm2V−1s−1 for pure C60 as the reference. High fill factors (FFs), power conversion efficiencies (PCEs), and open circuit voltages (VOC) were measured for PSC devices with C60–based ETLs, varying within the ranges of 0.892–0.897, 22.489–23.984 %, and 1.111–1.179 V, respectively, indicating they could yield excellent photovoltaic parameters.

Charge Trapping and Emission during Bias Temperature Stressing of Schottky Gate GaN-on-Silicon HEMT Structures Targeting RF/mm Wave Power Amplifiers.

For operation as power amplifiers in RF applications, high electron mobility transistor (HEMT) structures are subjected to a range of bias conditions, applied at both the gate and drain terminals, as the device is biased from the OFF- to ON-state conditions. The stability of the device threshold voltage (Vt) condition is imperative from a circuit-design perspective and is the focus of this study, where stresses in both the ON and OFF states are explored. We see rapid positive threshold voltage increases under negative bias stress and subsequent recovery (i.e., Vt reduces), whereas conversely, we see a negative Vt shift under positive stress and Vt increase during the subsequent relaxation phase. These effects are correlated with the thickness of the GaN layer and ultimately result from the deep carbon-acceptor levels in the C-GaN back barrier incorporated to screen the buffer between the silicon substrate and the epitaxially grown GaN layer. Methods to mitigate this effect are explored, and the consequences are discussed.

First-principles study of phase-dependent carrier transport mechanism for MASnI3 Sn-based halide perovskite

Organic-inorganic hybrid perovskites have attracted tremendous attentions owing to their excellent properties as next-generation photovoltaic devices. With soft covalent framework, organic-inorganic hybrid perovskites exhibit different phases at different temperatures. The band-edge features of perovskites are mainly contributed by inorganic framework, which means the structural differences between these phases would lead to complex carrier transport. We investigated the carrier transport of Sn-based organic-inorganic hybrid perovskite CH3NH3SnI3 (MASnI3), considering acoustic deformation potential scattering, ionized impurity scattering, and polar optical phonon scattering. It is found that the electron mobility of each phase of MASnI3 is strongly correlated with the Sn–I–Sn bond angle and there is in-plane/out-of-plane anisotropy. The projected crystal orbital Hamilton population analysis suggested that the tilt and rotation of the [SnI6]4− octahedron influence the Sn(p)–I(p) orbital electron coupling and the electron transport, leading to different band-edge features in multiple phases. The carrier mobility with respect to temperature was further calculated for each phase of MASnI3 in respective temperature intervals, showing lower carrier mobility in high temperature. Comparing the contribution of different scattering mechanisms, it was found that the dominant scattering mechanism is polar optical phonon scattering, while multiple scattering mechanisms compete in individual cases.

Towards first-principles predict of doped α-Ga2O3 based structural and electrical properties

The α-Ga2O3 holds significant research value on high power device applications for its superior breakdown voltage performance. However, research concerning the doping of α-Ga2O3 remains scant, and the optimal dopant remains unidentified. To identify a potential n-type dopant, a theoretical study of the effects of group IV atoms (Si, Ge, Sn) on doped α-Ga2O3 was evaluated through the first principles calculations. We have systematically explored the lattice deformation, band structure, density of state, charge density difference and electron localization functions. The electron mobility is then evaluated by the deformation potential theory. The lowest formation energy of the Si-doped system suggests it forms the most readily. Meanwhile, Si loses approximately 1.5 times more electrons than Ge and Sn in the doped α-Ga2O3, as evidenced by the charge density difference and electron localization functions. Furthermore, our results reveal that Si is a superior dopant over Ge and Sn. It is owing to a small interaction between the Si 3 s state and the Ga 4 s generated host CBM, resulting in a minimal effect on the CBM even at high doping levels. The findings of this study have important consequences for improving the doping process of α-Ga2O3 and achieving the development of optoelectronic devices.