Carrier Transport Behavior Research Articles

Al2B12C with High Ambipolar Mobility Driven by a Unique B-C Framework.

The development of materials with high ambipolar mobility is pivotal for advancing multifunctional applications, yet such materials remain scarce. Presently, cubic boron arsenide (BAs) stands out as the premier ambipolar material, demonstrating an ambipolar mobility of ∼1600 cm2 V-1 s-1 at room temperature [Science 2022, 377, 433 and Science 2022, 377, 437]. Herein, we illustrate that semiconducting Al2B12C, featuring a nonclathrate B-C framework in which a C atom bonds to the vertices of four distorted hexagonal antiprism B12 units via quasi-sp3 hybridization, is predicted to possess ambipolar carrier transport behavior. Its ambipolar mobility can reach up to ∼2095 cm2 V-1 s-1. The hole transport originates from the C pz orbitals that trap the electrons of Al atoms at the valence band maximum, forming a C-Al-C hole channel along the c-axis direction, whereas electron transport stems from the π electrons in B12 units. For Al2B12C, polar optical phonon scattering serves as the primary mechanism limiting mobility. Additionally, it displays a high absorption coefficient (105 cm-1) in the visible spectrum. These appealing properties make Al2B12C a highly promising environmentally friendly semiconductor for applications in electronics and photovoltaic devices.

Preparation of carbon dot/polyaniline composites as voltage based dielectric material for capacitor applications

Polyaniline-carbon dot (CD/PANI) composites were prepared via in-situ oxidative polymerization of aniline in the presence of carbon dots, with specific concentrations carefully controlled during synthesis. The composite was characterized using spectroscopic (FT-IR), morphological (TEM, SEM) and electrical methods. Impedance analysis was employed to investigate the transport behavior of charge carriers in the frequency range of 500 Hz to 10 MHz at 25 °C. This study provides a comprehensive analysis of the dielectric properties of the CD/PANI composite, including dielectric constant, dielectric loss, loss factor, AC conductivity, admittance, impedance, and Cole–Cole plots. The dielectric constant of the CD/PANI composite was 6.97 for 1 kHz at 0.5 V and 12.87 for 1 kHz at 5 V. The values indicate that the increase in the dielectric constant of nanocomposite with increasing voltage. This suggests that CD/PANI composite is a dielectric material whose dielectric constants are controlled by applied voltage. Notably, the dielectric constant increased with rising applied voltage and decreased with increasing frequency. Current-voltage (I-V) measurements revealed that the composite's dielectric parameters could be tuned by varying the applied DC voltage, suggesting its potential as a voltage-dependent dielectric (VDD) material for capacitor applications. Furthermore, the enhanced electrical conductivity indicates that the CD/PANI composite is a promising candidate for next-generation dielectric devices.

In-Device Ballistic-Electron-Emission Spectroscopy for Accurately In Situ Mapping Energy Level Alignment at Metal-Organic Semiconductors Interface.

Energy level alignment at metal/organic semiconductors (OSCs) interface governs electronic processes in organic electronics devices, making its precise determination essential for understanding carrier transport behaviors and optimizing device performance. However, it is proven that accurately characterizing the energy barrier at metal/OSC interface under operational conditions remains challenging due to the technical limitations of traditional methods. Herein, through integrating highly-improved device constructions with an ingenious derivative-assisted data processing method, this study demonstrates an in-device ballistic-electron-emission spectroscopy using hot-electron transistors to accurately characterize the energy barrier at metal/OSC interface under in-operando conditions. This technique is found that a remarkable improvement in measurement accuracy, reaching up to ±0.03eV, can be achieved-surpassing previous techniques (±0.1-0.2eV). The high accuracy allows us to monitor subtle changes in energy barriers at metal/OSC interface caused by variations in the aggregation state of OSCs, a phenomenon that is theoretically possible but failed to be directly demonstrated through conventional methods. Moreover, this study makes demonstration that this technology is universally applicable to various metal/OSC interfaces consisting of electron-transporting, hole-transporting, and ambipolar OSCs. These findings manifest the great potential of this method to advance both theoretical exploration and technical applications in organic electronics.

Defect Engineering Advances Thermoelectric Materials.

Defect engineering is an effective method for tuning the performance of thermoelectric materials and shows significant promise in advancing thermoelectric performance. Given the rapid progress in this research field, this Review summarizes recent advances in the application of defect engineering in thermoelectric materials, offering insights into how defect engineering can enhance thermoelectric performance. By manipulating the micro/nanostructure and chemical composition to introduce defects at various scales, the physical impacts of diverse types of defects on band structure, carrier and phonon transport behaviors, and the improvement of mechanical stability are comprehensively discussed. These findings provide more reliable and efficient solutions for practical applications of thermoelectric materials. Additionally, the development of relevant defect characterization techniques and theoretical models are explored to help identify the optimal types and densities of defects for a given thermoelectric material. Finally, the challenges faced in the conversion efficiency and stability of thermoelectric materials are highlighted and a look ahead to the prospects of defect engineering strategies in this field is presented.

The Construction and Mechanism Study of High-Speed Carrier Transport Channel in Gallium Arsenide Homojunction Toward High-Performance Photoelectrochemical Photodetector.

The energy band structure and surface/interface properties are prerequisite for not only preserving the intrinsic material quality but also manipulating carrier transport behavior for photoelectrochemical (PEC) photodetection. How to precisely design/regulate the band structure and surface/interface properties of semiconductor materials is the key to improving the performance of PEC photodetection. Herein, the quintuple heterotypic homojunction (QH) GaAs film is fabricated with a gradient energy band via plasma-assisted molecular beam epitaxy for constructing a high-speed carrier transport channel in PEC photodetection, which can efficiently drive the separation and transport of photogenerated electron-hole pairs. The designed QH-GaAs-based PEC photodetector exhibits excellent performances, compared with bare i-GaAs, delivering an ultrashort rise/decay times of only 1.1/1.1ms and a high responsivity of 20.4mAW-1 at 0V under 850nm illumination. Strikingly, an ultrahigh detectivity with 1.46×1012 Jones is achieved. More importantly, the QH-GaAs device can stably operate underwater seawater environment. This study provides a novel strategy for designing and fabricating multiple heterotypic homojunction with gradient energy band to boost charge transport dynamics for PEC fields.

A Review of Wide Bandgap Semiconductors: Insights into SiC, IGZO, and Their Defect Characteristics.

Although the irreplaceable position of silicon (Si) semiconductor materials in the field of information has become a consensus, new materials continue to be sought to expand the application range of semiconductor devices. Among them, research on wide bandgap semiconductors has already achieved preliminary success, and the relevant achievements have been applied in the fields of energy conversion, display, and storage. However, similar to the history of Si, the immature material grown and device manufacturing processes at the current stage seriously hinder the popularization of wide bandgap semiconductor-based applications, and one of the crucial issues behind this is the defect problem. Here, we take amorphous indium gallium zinc oxide (a-IGZO) and 4H silicon carbide (4H-SiC) as two representatives to discuss physical/mechanical properties, electrical performance, and stability from the perspective of defects. Relevant experimental and theoretical works on defect formation, evolution, and annihilation are summarized, and the impacts on carrier transport behaviors are highlighted. State-of-the-art applications using the two materials are also briefly reviewed. This review aims to assist researchers in elucidating the complex impacts of defects on electrical behaviors of wide bandgap semiconductors, enabling them to make judgments on potential defect issues that may arise in their own processes. It aims to contribute to the effort of using various post-treatment methods to control defect behaviors and achieve the desired material and device performance.

Signature of electrothermal transport in 18 nm vertical junctionless gate-all-around nanowire field effect transistors

Abstract Addressing temperature hot-spots resulting from self-heating effects (SHE) poses a significant challenge in the design of emerging nanoscale transistors, such as vertical junctionless nanowire field-effect transistors (VNWFETs), due to reduced thermal conductivity. Consequently, electrothermal modeling becomes crucial for a comprehensive understanding of the underlying physical mechanisms governing carrier degradation and thermal conduction in these nanoscale devices. In this study, we present an enhanced drift-diffusion model coupled with nonlocal Guyer-Krumhansl (GK) equations to accurately capture carrier-phonon interactions and explore the electrothermal characteristics of gate-all-around (GAA) VNWFETs. Pulsed current-voltage (I–V) measurements are employed to investigate the performance of a state-of-the-art 18nm VNWFET technology. Furthermore, we report on the influences of both trapping and SHE under high-bias conditions for varying pulse widths. Our findings reveal that optimization of mobility degradation mechanisms allows for improved control over the physical behavior of carrier transport in these emerging technologies. Through careful consideration of these factors, it becomes possible to enhance the overall performance of GAA VNWFETs, particularly in mitigating temperature hot-spots and addressing challenges associated with self-heating effects.

Room-temperature self-calibrating sensor based on CsPbBr3/SnO2 for detecting low-concentration sulfur dioxide

Sulfur dioxide (SO2) is a colorless toxic gas, and accurate monitoring of its concentration is important for safety. However, accuracy is often interfered by humidity. To address the issues, in this work, a self-calibrating SO2 sensor based on CsPbBr3/SnO2 was prepared, the sensor exhibited an excellent response to parts per billion (ppb) levels of SO2 at room temperature, which is rarely achieved by other SO2 sensors. The response sensitivity of the sensor to 600 ppb SO2 reached up to 0.53 with response/recovery times of 17/285 s. In addition, the CsPbBr3/SnO2-based SO2 gas sensor showed a low detection limit, good reproducibility, and high selectivity. Moreover, theoretical calculations show that the gas recognition mechanism is attributed to the significant changes in the band structure and density of states of the heterojunction materials CsPbBr3/SnO2 after gas adsorption, thereby altering the charge carrier transport behavior and electrical properties. A self-calibrating algorithm MobileNetV2 was employed to eliminate humidity interference and effectively identify low-concentration SO2 in humid environments, and the recognition accuracy rate is 0.85. This work demonstrates the production of a high-performance SO2 gas sensor, and provides an effective method to eliminate the interference of humidity, making it significant in environmental monitoring and air quality control.

Unveiling the Carrier Dynamics of Perovskite Light-Emitting Diodes via Transient Electroluminescence.

Perovskite light-emitting diodes (PeLEDs) have garnered significant attention due to their outstanding optoelectronic properties. However, investigating carrier transport and recombination behavior during device operation poses persistent challenges. In this study, we explore the impact of additive and interface engineering on device performance using transient electroluminescence (TREL). Polyethylene glycol (PEG) induces the formation of square-faceted nanocrystals with a homogeneous size distribution and extended fluorescence lifetime. Consequently, these PeLEDs exhibit remarkable stability. Additionally, employing an electron transport layer of 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine (PO-T2T), which has a better match to the energy bands of the perovskite layer and a higher carrier mobility, allows for lower turn-on voltage and faster response but also suffers from a short decay time and poor stability. Moreover, low-temperature TREL characterization shows that the carrier mobility is also significantly suppressed with decreasing temperature, which reduces the transient response speed.

Temperature-induced activation and reversal of the relativistic ratchet currents on a graphene chip model

We investigate a monolayer graphene chip’s relativistic ratchet current (RRC). Our findings indicate that thermal noise can paradoxically amplify the RRC, in contrast to its conventional inhibitory role. Under noise, temperature (T) activation of the RRC remains stable over a broader range of T values, and an increased number of RRCs reversals are observed as a function of T and relevant parameters of the external electric field. The results regarding structural changes and symmetry breaking of the dissipative attractors can be understood. The observed activation and reversal of RRCs under a variation of external parameters unveil the diverse and complex behavior of the charge carrier transport on the graphene chip. Understanding this behavior allows for generating specific RRCs values, properties and effects for the charge carriers, offering a variety of possibilities for application and control of the graphene chip device.

Strategic Buried Defect Passivation of Perovskite Emitting Layers by Guanidinium Chloride for High-Performance Pure Blue Perovskite Light Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) show promise for high-definition displays due to their exceptional electroluminescent properties. However, the performance of pure blue PeLEDs is hindered by the unfavorable ionic behavior of halides and the presence of defective antisites in blue-emitting perovskite materials. An unstable buried interface between charge transport layers and the perovskite emitting layer is a major issue that limits carrier transport and recombination behavior in PeLEDs. In this study, effective buried defect passivation of pure blue perovskite emitting layers by introducing guanidinium chloride (GACl) as a bottom-passivating layer is demonstrated. The GACl bottom layer not only passivates the point defects present at the buried interface but also provides chloride anions to suppress ion migration and halide vacancy formation. Along with the defect passivation, GACl also enforces phase purity of 2D layered structure in the perovskite emitting layers to improve crystallinity and optoelectronic properties. As a result, the PeLEDs with high brightness (1200cd m-2) and excellent external quantum efficiency (6.61%) are achieved at a spectrally stable pure blue electroluminescence at 471nm (band width = 17.63nm). This study offers insights into the straightforward way for effective buried passivation for preparing high-performance PeLEDs.

Solution‐Processed Sb2(S,Se)3 Seed‐Assisted Sb2Se3 Thin Film Growth for High Efficiency Solar Cell

Antimony selenide (Sb2Se3) emerges as a promising sunlight absorber in thin film photovoltaic applications due to its excellent light absorption properties and carrier transport behavior, attributed to the quasi‐one‐dimensional Sb4Se6‐nanoribbon crystal structure. Overcoming the challenge of aligning Sb2Se3‐nanoribbons normal to substrates for efficient photogenerated carrier extraction, a solution‐processed nanocrystalline Sb2(S,Se)3‐seeds are employed on the CdS buffer layer. These seeds facilitate superstrated Sb2Se3 thin film solar cell growth through a close‐space sublimation approach. The Sb2(S,Se)3‐seeds guided the Sb2Se3 absorber growth along a [002]‐preferred crystal orientation, ensuring a smoother interface with the CdS window layer. Remarkably, Sb2(S,Se)3‐seeds improve carrier transport, reduce series resistance, and increase charge recombination resistance, resulting in an enhanced power conversion efficiency of 7.52%. This cost‐effective solution‐processed seeds planting approach holds promise for advancing chalcogenide‐based thin film solar cells in large‐scale manufacturing.

Organic Ligand Engineering for Tailoring Electron-Phonon Coupling in 2D Hybrid Perovskites.

In the emerging two-dimensional organic-inorganic hybrid perovskites, the electronic structures and carrier behaviors are strongly impacted by intrinsic electron-phonon interactions, which have received inadequate attention. In this study, we report an intriguing phenomenon of negative carrier diffusion induced by electron-phonon coupling in (2T)2PbI4. Theoretical calculations reveal that the electron-phonon coupling drives the band alignment in (2T)2PbI4 to alternate between type I and type II heterostructures. As a consequence, photoexcited holes undergo transitions between the organic ligands and inorganic layers, resulting in abnormal carrier transport behavior compared to other two-dimensional hybrid perovskites. These findings provide valuable insights into the role of electron-phonon coupling in shaping the band alignments and carrier behaviors in two-dimensional hybrid perovskites. They also open up exciting avenues for designing and fabricating functional semiconductor heterostructures with tailored properties.

Analytical models of the electric field and carrier transit time in the base of bipolar junction transistors

The conventional theory of the bipolar junction transistor (BJT) does not clarify the electric field and its effect on the carrier transit in the uniformly doped base region, although the electric field is considered to be a second-order effect at high-level injection. In this study, analytical models of the carrier distribution, electric field, and carrier transit time in the base region are developed without making additional assumptions. It is found that the electric field may change direction, from forward to reverse, as long as the injection level reaches a criterion, affecting the carrier transport behavior. The models are based on the renovated p–n junction theory, provide insight into the carrier transit and are able to cover all levels of injection without the need to handle the low- and high-level injection separately. These models hold significance in retrieving the theoretical integrity of bipolar junction devices, and can be useful for further investigation in structure design, capacitance control, and AC performance optimization of the p–n junction-based device.

Performance improvement of GaN-based vertical cavity surface emitting laser by employing a hole storage layer and enhancing the carrier transport behavior

In this paper, the transport behavior of carriers between multiple quantum wells (vertical) and inside a single quantum well (radial) in a GaN-based Vertical Cavity Surface Emitting Laser (VCSEL) is investigated, and a new device structure with a hole storage layer is proposed to enhance the laser performance. The theoretical results indicate that the vertical transport capability of holes is the key factor for total stimulated recombination rate and hole leakage. The VCSEL with a double-QW structure exhibits better output performance compared to the devices with three or more QWs owing to the lower light absorption loss and the stronger optical field in the active region. Furthermore, a thicker undoped GaN layer is proposed to be added as the hole storage layer to mitigate hole leakage for the VCSEL with a double-QW structure. This new structure can increase the tilt of energy band in the region of the hole storage layer and effectively improve the uniformity of radial distribution of holes in QWs. Therefore, it is beneficial to reduce the threshold current and enhance the laser output power.

Enhanced power factor and figure of merit through magnesium doping in Sb2Si2Te6

We report here a high thermoelectric performance in magnesium (Mg) doped Sb2Si2Te6. The substitution of Mg2+ for Sb3+ in Sb2Si2Te6 induces a synergetic effect on electrical transport performance, exciting multi-band carrier transport behavior, enhancing carrier concentration, and increasing the density of states effective mass. Such effects lead to the highest power factor of 10.95 μW cm−1 K−2 at 824 K for the Sb1.99Mg0.01Si2Te6, representing a ∼22 % increase compared to pristine Sb2Si2Te6. In addition, Mg doping induces MgSb− point defects phonon scattering, resulting in a low thermal conductivity of ∼0.52 W m−1 K−1 at 824 K. The simultaneous optimization of the power factor and thermal conductivity in Sb1.99Mg0.01Si2Te6 leads to a peak ZT of ∼1.15 at 824 K and an average ZT of ∼0.68 (400−824 K), showing its potential for power generator at medium temperature.

Biocompatible Metal-Free Perovskite Membranes for Wearable X-ray Detectors.

Halide perovskites are emerging as promising materials for X-ray detection owing to their compatibility with flexible fabrication, cost-effective solution processing, and exceptional carrier transport behaviors. However, the challenge of removing lead from high-performing perovskites, crucial for wearable electronics, while retaining their superior performance, persists. Here, we present for the first time a highly sensitive and robust flexible X-ray detector utilizing a biocompatible, metal-free perovskite, MDABCO-NH4I3 (MDABCO = methyl-N'-diazabicyclo[2.2.2]octonium). This wearable X-ray detector, based on a MDABCO-NH4I3 thick membrane, exhibits remarkable properties including a large resistivity of 1.13 × 1011 Ω cm, a high mobility-lifetime product (μ-τ) of 1.64 × 10-4 cm2 V-1, and spin Seebeck effect coefficient of 1.9 nV K-1. We achieve a high sensitivity of 6521.6 ± 700 μC Gyair-1 cm-2 and a low detection limit of 77 nGyair s-1, ranking among the highest for biocompatible X-ray detectors. Additionally, the device exhibits effective X-ray imaging at a low dose rate of 1.87 μGyair s-1, which is approximately one-third of the dose rate used in regular medical diagnostics. Crucially, both the MDABCO-NH4I3 thick membrane and the device showcase excellent mechanical robustness. These attributes render the flexible MDABCO-NH4I3 thick membranes highly competitive for next-generation, high-performance, wearable X-ray detection applications.

Dual Alloying Enables High Thermoelectric Performance in AgSbTe2 by Manipulating Carrier Transport Behavior

AbstractAgSbTe2 exhibits superior thermoelectric performance in the mid‐temperature region, but its electrical properties are strongly affected by intrinsic defects and secondary phases. Distinctively, the high mobility electrons still play an important role as minority carriers in p‐type AgSbTe2 even below the bipolarization temperature and decrease the Seebeck coefficient. Here, the Al and Se dual alloying can effectively increase the hole concentration by reducing the cation vacancy formation energy and simultaneously reduce the electron concentration by suppressing the n‐type Ag2Te secondary phase are demonstrated, which results in the shift of carrier transport from two‐type to one‐type as confirmed by Hall measurement. Consequently, through adjusting the ratio of hole and electron conductivity, the average power factor of alloyed sample is enhanced by 70%. Combined with further reduced lattice thermal conductivity resulting from high‐density stacking faults and superstructures, a maximum zT of 1.90 and an average zT of 1.42 are obtained in the temperature range of 323 to 623 K in the (AgSbTe2)0.98(AgAlSe2)0.02 sample. Finally, based on the finite element analysis modeling results, both single‐leg and double‐leg thermoelectric devices are fabricated, which show high conversion efficiency of 11.2% and 5.2%, respectively.

Epitaxial Tantalum‐Doped β‐Ga2O3 Thin Films Grown on Mgo (001) Substrate by Pulsed Laser Deposition

Epitaxial thin films of tantalum‐doped β‐Ga2O3 (Ta‐Ga2O3) are grown on MgO (001) substrates to study the effect of Ta doping on the electrical properties of β‐Ga2O3 films. X‐Ray diffraction (XRD) measurements show that the films with different Ta doping concentrations are (00l)‐oriented single‐crystalline β‐Ga2O3 without impurity phases. The incorporation of the Ta element modifies the electrical properties of Ta‐Ga2O3 films significantly. At a very low doping ratio of 0.05 mol%, the Ta‐Ga2O3 film showed a minimum resistivity of 2.32 Ω cm and a carrier concentration of 2.48 × 1017 cm−3. The corresponding activation energy of Ta element in the film is 16.8 meV, suggesting that the Ta element is a promising shallow donor dopant. The X‐ray photoelectron spectroscopy (XPS) analysis confirms that the Fermi level of the Ga2O3 films shifts toward the conduction band minimum after the introduction of Ta ions. These results indicate that the transition metal element Ta could be an effective n‐type dopant for modulating the carrier transport behavior of β‐Ga2O3 films.

Investigations of Morphology and Carrier Transport Characteristics in High‐Performance PEDOT:PSS/Tellurium Binary Composite Fibers Produced via Continuous Wet‐Spinning

AbstractFiber‐based flexible thermoelectric (TE) generators are highly desirable due to their capability to convert thermal energy into electricity and their potential applications in wearable electronics. High‐performance poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Tellurium (Te) composite TE fibers have been successfully developed via a continuous wet‐spinning approach followed by sulphuric acid treatment. With a simple pre‐modification to Te nanowires, the inorganic Te fillers form uniform distribution in PEDOT:PSS. At the optimal condition, the composite fibers exhibit a power factor of 233.5 µW m−1 K−2 and mechanical strength of 205 MPa, which are among the highest values reported so far for the PEDOT:PSS‐based TE fibers. From the viewpoint of TE property enhancement mechanism, understanding the morphology and carrier transport behavior in the 1D organic/inorganic composite fibers remains still challenging. On basis of a series of PEDOT:PSS/Te composite fibers with varying Te fractions, orientations of both the inorganic and organic constituents are quantitatively evaluated. Their electrical conductivities and Seebeck coefficients are also analyzed with modified series‐parallel models and energy filtering theory. This work may not only provide a universal approach to produce high‐performance organic/inorganic composite TE fibers for various wearable applications, but also help to understand the morphology and charge transport between heterogeneous phases in a 1D composite.