Carrier Mobility Research Articles

Passivation of Germanium Surfaces by HF:H2O2 Aqueous Solution

Promising intrinsic electronic properties, such as narrow bandgap and high charge carrier mobilities, make germanium (Ge) a good replacement for silicon in optoelectronic applications (e.g., photodetectors). However, successful fabrication of efficient Ge devices requires minimization of both reflectance and surface recombination losses. This work begins with an observation that metal‐assisted chemical etching (MACE) of Ge surfaces, used for optics improvement, reduces surface recombination without application of any intentional passivation. We proceed with investigation of the effect of MACE solution components and their mixtures on Ge surface passivation. The results demonstrate that HF:H2O2 aqueous solution leads to efficient and stable passivation. The film formed in this solution secures surface recombination velocity (Seff) of 14 cm s−1. Morphological and chemical characterization of the structure reveals porous germanium (PGe) layer with some GeOx included. Finally, we propose several hypotheses on a mechanism behind this passivation, among which are the presence of GeO2 at the film‐bulk Ge interface and appearance of a potential barrier due to the heterojunction formation. The presented Ge passivation with PGe layer provides a simple and cost‐efficient alternative to existing state‐of‐the‐art passivation schemes.

Correlating the low-temperature photoluminescence with electron transport properties in cerium oxide thin film.

The complex interaction between the intrinsic and extrinsic state variables of strongly correlated insulator thin films is drawing interest as it shows memristive behavior that may be applicable to neuromorphic computing. Cerium oxide is an interesting material as its band structure is modified due to the formation of oxygen vacancy defects. The polaron formation that results from the reduction of the Ce4+ state to the Ce3+ state through oxygen vacancies is crucial for the electron transport in cerium oxide and is strongly influenced by temperature. In this work, we examined the relationship between the change in band structure and the associated conductivity at lower temperatures when ceria is exposed to light. Following light excitation, the creation of oxygen vacancies results in electron localization in the Ce 4f state, followed by the electron transition from 4f1 to 4f0, generating the PL spectra. With decreasing temperature, the lattice vibration decreases, and the splitting in the PL peak at a particular energy state validates the weaker electron-phonon interaction with an exciton trap. This reduces the carrier mobility of the film as observed from the resistance vs temperature curve of ceria under dark conditions. When excited by a particular energy of light, the electrons move more easily from the defect state to the conduction band, increasing conductivity at much lower temperatures than the conductivity under dark conditions.

Integration of Boron Nitride Into Tin‐Enriched SnSe2 for a High‐performance Thermoelectric Nanocomposite with Optimized Electrical Transport and Mechanical Properties

AbstractThermoelectric materials with high figures of merit are essential for efficient energy conversion and cooling applications. This study integrates boron nitride (BN) into tin‐enriched SnSe₂ to form a multi‐phase composite with synergistic thermoelectric and mechanical properties. The incorporation of BN into SnSe2 offers the dual benefit of optimizing both carrier concentration and carrier mobility. Notably, the BN/SnSe2 composite exhibits a significant increase in the Seebeck coefficient, attributed to an increased bandgap and electronic density of states near the Fermi level, as corroborated by density functional theory calculations. Consequently, an impressive power factor of 940 µWm−1K−2 is achieved for the sample with a mere 0.8 wt.% BN content. This power factor enhancement, coupled with a notable ≈37% reduction in lattice thermal conductivity due to increased phonon scattering from lattice strain induced by Se vacancies, contributes to a remarkable ZTmax value of 0.68 at 767 K, exceeding the performance of pristine SnSe2 by ≈76%. Additionally, BN enhances stress distribution and deformation behavior, improving stability and reliability under diverse thermal and mechanical conditions. This study demonstrates an effective approach for advancing SnSe₂ thermoelectric materials and provides a foundation for composite design and energy band engineering to achieve high‐performance thermoelectric devices.

Study of Grain Boundary: From Crystallization Engineering to Machine Learning

Grain boundaries play a vital role in determining the structural, functional, mechanical, and electrical properties of semiconductor materials. Recent studies have yielded great advances in understanding and modulating the grain boundaries via semiconductor crystallization engineering and machine learning. In this article, we first provide a review of the miscellaneous methods and approaches that effectively control the nucleation formation, semiconductor crystallization, and grain boundary of organic semiconductors. Using the benchmark small molecular semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) as a representative example, the crystallization engineering methods include polymer additive mixing, solvent annealing, gas injection, and substrate temperature control. By studying the grain-width-dependent charge transport, we propose a grain boundary model as a fundamental basis to theoretically understand the intrinsic relation between grain boundary engineering and charge carrier mobility. Furthermore, we discuss the various machine learning algorithms and models used to analyze grain boundaries for the various important traits and properties, such as grain boundary crystallography, energy, mobility, and dislocation density. This work highlights the unique advantages of both crystallization engineering and machine learning methods, demonstrates new insights into discovering the presence of grain boundaries and understanding new properties of materials, and sheds light on the great potential of material application in various fields, such as organic electronics.

Composite and Nanocomposite Thin-film Structures Based on Chitosan Succinamide

Aim: Currently, developing composite and nanocomposite materials based on natural polymers is attracting the growing attention of scientists. In particular, chitosan succinamide, a modified biopolymer, has good biocompatibility, biodegradability, and electrical conductivity, allowing it to be used as a functional material for creating various electronic devices, including sensors for use in medicine and pharmaceuticals. Composite sensors based on chitosan deriva-tives have found application for the recognition and determination of enantiomers of tryptophan, tyrosine, naproxen, and propranolol in human urine and blood plasma in tablet forms of drugs without a preliminary active substance. Methods: This article discusses the studies on composite and nanocomposite thin-film structures based on chitosan succinamide obtained using various fillers, such as graphene oxide, single-walled carbon nanotubes, and carbon adsorbents. Result: The studies used cyclic voltammetry, electrochemical impedance spectroscopy, and atom-ic force microscopy. The results created field-effect transistors based on the films in question as the transport layer. Conclusion: The mobility of charge carriers was estimated, and the following values were ob-tained: μ(SCTS) = 0.173cm2/V·s; μ(SCTS-GO) = 0.509 cm2/V·s; μ(SCTS-CP) = 0.269 cm2/V·s; μ(SCTS-CB) = 0.351cm2/V·s; μ(SCTS-SWCNT) = 0.713 cm2/V·s.

Modulating carrier mobility of N-doped rGO for flexible linear temperature sensors

Modulating carrier mobility of N-doped rGO for flexible linear temperature sensors

Enhanced carriers mobility of Te atomic chain encapsulated in nanotubes

Enhanced carriers mobility of Te atomic chain encapsulated in nanotubes

Heusler-based topological quantum catalyst Fe2VAl with obstructed surface states for the hydrogen-evolution reaction

Topological materials are widely esteemed for their surface metallic states and remarkable carrier mobility, making them effective catalysts for heterogeneous processes. This study showcases the outstanding properties of Fe2VAl, an experimentally prepared compound that enjoys a Cu2MnAl-type Heusler structure. It specifically highlights the presence of robust obstructed surface states on the (001) surface and the outstanding catalytic effectiveness of the compound in electrochemical hydrogen evolution processes (HER). The band structure calculation in this work shows that it is an obstructed atomic semimetal with a pseudo-gap of -0.088 eV (nearly -0.1 eV). These findings align with the previous optical conductivity measurements conducted at low temperatures, which also showed a similar pseudo-gap. This work suggests that the easily prepared Fe2VAl compound may be an excellent topological quantum material for topological catalysis.

Light and Carrier Transportation Management in Transparent Electrode for Achieving over 30% Efficiency Perovskite/Silicon Tandem Solar Cells.

Perovskite/silicon tandem solar cells have drawn widespread attention owing to their higher power conversion efficiency (PCE). However, reducing the reflection and parasitic absorption as much as possible in the transparent electrode is of considerable interest to promote the tandem device to obtain higher circuit current density (JSC). Furthermore, the carrier vertical and lateral transport capability of transparent electrodes also affects the electrical performance of solar cells. Herein, we designed and realized a stacked structure of a columnar-equiaxed zirconium-doped indium oxide (IZrO) film. The optimal stacked IZrO thin film shows carrier density and mobility of 9.4 × 1020 cm-3 and 29.7 cm2 V-1 s-1, respectively. Additionally, it also shows superior optical transmittance and lower parasitic absorption in the visible-to-near-infrared region. In addition, reflectance in the perovskite/c-Si tandem solar cell shows an obvious reduction after the application of a stacked IZrO transparent electrode because of the gradient refractive index. Finally, the stacked IZrO transparent electrode was incorporated into P-I-N-type perovskite/textured-silicon tandem solar cells, and the champion stacked IZrO-based device showed PCE of 30.12% with an active area of 1.05 cm2.

Role of Superlattice Phonons in Charge Localization Across Quantum Dot Arrays.

Understanding charge transport in semiconductor quantum dot (QD) assemblies is important for developing the next generation of solar cells and light-harvesting devices based on QD technology. One of the key factors that governs the transport in such systems is related to the hybridization between the QDs. Recent experiments have successfully synthesized QD molecules, arrays, and assemblies by directly fusing the QDs, with enhanced hybridization leading to high carrier mobilities and coherent band-like electronic transport. In this work, we theoretically investigate the electron transfer dynamics across a finite CdSe-CdS core-shell QD array, considering up to seven interconnected QDs in one dimension. We find that, even in the absence of structural and size disorder, electron transfer can become localized by the emergent low-frequency superlattice vibrational modes when the connecting neck between QDs is narrow. On the other hand, we also identify a regime where the same vibrational modes facilitate coherent electron transport when the connecting necks are wide. Overall, we elucidate the crucial effects of electronic and superlattice symmetries and their couplings when designing high-mobility devices based on QD superlattices.

Integrative Enhancement of Energy‐Level Alignment and Defect Passivation for High‐Performance Lead‐Free Perovskite Solar Cells

AbstractCsGeI2Br‐based perovskites with a favorable bandgap and high absorption coefficient, show great promise as candidates for efficient lead‐free perovskite solar cells (PSCs). However, the significant defect recombination and energy alignment mismatch at the perovskite‐transport layer interface limit both the device's performance and long‐term stability. To overcome these challenges, the photovoltaic potential of the device is unlocked by optimizing the optical and electronic parameters through a rigorous numerical simulation, including the transport layer materials, doping density, bulk/interface defect density, and carrier mobility. As a result, the optimized device achieved a champion power conversion efficiency of 28.00%. To further elucidate the inherent physical behavior, the activator energy of carrier recombination, along with the conduction and valence band offsets, are also investigated. Additionally, different types of device structures, including p‐i‐n and HTL‐free structures, are briefly examined. Finally, a detailed roadmap for enhancing the efficiency of the device is proposed, offering valuable insights for improving inorganic lead‐free CsGeI2Br perovskite solar cells in optoelectronic applications.

Dual Roles of PTSA in Electrical Conductivity of PEDOT:PTSA with Large Seebeck Coefficient

The electrical conduction mechanism of PEDOT:PTSA thermoelectric conversion material supported on PET fiber was investigated with varying PTSA concentrations. Raman analysis revealed that an increasing PTSA concentration promoted transformation from a benzoid to a quinoid structure in PEDOT chains, reaching saturation in higher concentrations. All samples exhibited p-type behavior, with Seebeck coefficients ranging from 0.9 to 2.7 mV/K. The temperature dependence of electrical conductivity showed that conductivity and activation energy exhibited extreme values with increasing PTSA concentration, correlating with the saturation of quinoid structure transformation. This behavior suggests that PTSA serves dual roles: at lower concentrations, it enhances electrical conductivity through chemical doping, increasing carrier concentration and mobility via quinoid structure formation; at higher concentrations, excess PTSA induces carrier scattering without contributing to chemical doping, thereby reducing conductivity. These findings indicate that the thermoelectric properties of PEDOT:PTSA on PET fiber are governed by the balance between chemical doping effects and carrier scattering mechanisms, which are both influenced by PTSA concentration.

Highly tunning of dielectric and photocatalytic properties of crystalline ZnO semiconductor: Functionality of Ba additives

Abstract In the present work, the concentration of Ba-additive played a significant role in advancing the dielectric properties and photo-removal activity of ZnO semiconductor for methylene blue dye. Ba doped ZnO semiconductor with different doping concentrations (Zn1-xBaxO, x = 0.003, 0.005, 0.007 and 0.009 wt.%) were grown by solid-state reaction route. The X-ray diffraction (XRD) data confirmed the formation of the wurtzite structure of ZnO along with the presence of BaO-based secondary phase (SP). The XRD peak intensity related to the SP was found to increase with the increase of Ba concentration. Microstructural analyses through scanning electron microscope (SEM) images and energy-dispersive X-ray analysis (EDS) showed that with the addition of Ba, a gradual increase in the grain size was observed. Furthermore, SP segregated at the grain boundary and showed an increasing trend with doping. The emergence of secondary phases with Ba concentration was confirmed with the help of supplementary spectroscopic characterizations including Fourier transform infrared spectroscopy (FTIR) and UV-Vis diffuse reflectance. The presence of BaO secondary phase has shown a benefit effect on the dielectric and photodegradation properties of ZnO material. The remarkable resistance reduction suggested that the higher Ba concentrations significantly enhance charge carrier mobility. For wastewater treatment uses, BZO9 photocatalyst exhibited a perfect degradation efficiency of 90.1% for methylene blue (MB) removal after 210 min of visible light illumination.

Transient Photoluminescence Reveals the Dynamics of Injected Charge Carriers in Perovskite Light-Emitting Diodes.

Understanding the dynamics of injected charge carriers is crucial for the analysis of the perovskite light-emitting diode (PeLED) operation. The behavior of the injected carriers largely dictates the external quantum efficiency (EQE) roll-off at high current densities and the temperature dependence of the EQE in PeLEDs. However, limitations such as sample capacitance and external circuitry hinder precise control of carrier injection rates, making it challenging to directly track the dynamics of individual carriers. Here, we explore the recombination dynamics of injected charge carriers in a small-grain methylammonium lead iodide (MAPI) PeLED pumped at high current densities by investigating the dynamics of additional carriers photogenerated by ultrashort optical pulses. We show that photogenerated charge carriers predominantly recombine in a geminate fashion within a single perovskite grain. Conversely, recombination between photogenerated and injected carriers is rare, even at current densities up to 100 A/cm2, due to the spatial separation caused by the internal electric field, which confines injected carriers near opposite electrodes. This spatial separation is a key mechanism behind the EQE roll-off in PeLEDs, with reduced carrier mobility at lower temperatures, mitigating this effect by weakening carrier localization and electron-hole separation.

Imine-Based Polymeric Mixed Ionic-Electronic Conductors Featuring Degradability and Biocompatibility for Transient Bioinspired Electronics.

Degradable features are highly desirable to advance next-generation organic mixed ionic-electronic conductors (OMIECs) for transient bioinspired artificial intelligence devices.It is highly challenging that OMIECs exhibit excellent mixed ionic-electronic behavior and show degradability simultaneously.Specially,in OMIECs,doping is often a tradeoff between structural disorder and charge carrier mobilities. Here, we describe a regiochemistry-driven backbone curvature approach to prepare OMIECs, enabling doped state ordered within efficient ionic-electronic conduction in organic electrochemical transistors (OECTs) and presenting degradable characteristics. Significantly, i-3gTIT shows an outstanding mobility (1.99 cm2 V-1 s-1) and μC* (302 F V-1 cm-1 s-1), and presents higher disorder-tolerance upon doping and faster degradation behavior than its regioisomer, o-3gTIT. Especially, the resulting OECT-based inverter shows a high voltage gain of 31.6 V V-1 at a low driving voltage of 0.6 V. Moreover, we demonstrate an application of transient OECT, i.e., biodegradable solid-state electrolyte of OECT-based artificial synapses. Remarkably, the regiochemistry-driven film crystallinity modulation enables the conversion from volatile to non-volatile operation in such synapses. The transient synapse based on i-3gTIT achieves over 90% recognition accuracy for small digit handwritten images, showing potential in security neuromorphic computing. Our work is the first presentation enabling excellent mixed conduction of OMIECs with degradable features for transient bioinspired electronics.

Imine‐Based Polymeric Mixed Ionic–Electronic Conductors Featuring Degradability and Biocompatibility for Transient Bioinspired Electronics

Degradable features are highly desirable to advance next‐generation organic mixed ionic−electronic conductors (OMIECs) for transient bioinspired artificial intelligence devices.It is highly challenging that OMIECs exhibit excellent mixed ionic‐electronic behavior and show degradability simultaneously.Specially,in OMIECs,doping is often a tradeoff between structural disorder and charge carrier mobilities. Here, we describe a regiochemistry‐driven backbone curvature approach to prepare OMIECs, enabling doped state ordered within efficient ionic‐electronic conduction in organic electrochemical transistors (OECTs) and presenting degradable characteristics. Significantly, i‐3gTIT shows an outstanding mobility (1.99 cm2 V‐1 s‐1) and μC* (302 F V‐1 cm‐1 s‐1), and presents higher disorder‐tolerance upon doping and faster degradation behavior than its regioisomer, o‐3gTIT. Especially, the resulting OECT‐based inverter shows a high voltage gain of 31.6 V V‐1 at a low driving voltage of 0.6 V. Moreover, we demonstrate an application of transient OECT, i.e., biodegradable solid‐state electrolyte of OECT‐based artificial synapses. Remarkably, the regiochemistry‐driven film crystallinity modulation enables the conversion from volatile to non‐volatile operation in such synapses. The transient synapse based on i‐3gTIT achieves over 90% recognition accuracy for small digit handwritten images, showing potential in security neuromorphic computing. Our work is the first presentation enabling excellent mixed conduction of OMIECs with degradable features for transient bioinspired electronics.

Bioinspired Chestnut Burr-like Polyaniline: Achieving Superhydrophobicity and Excellent Microwave Transparency through Controlled Polymerization.

Achieving dual functionalities of hydrophobicity and excellent microwave transmission in a single material remains a significant challenge, especially for advanced applications in aerospace, telecommunications, and navigation engineering. Inspired by natural designs like chestnut burrs, bioinspired polyaniline (PANI) particles with tunable micro-/nanostructures through a facile template-free polymerization process have been developed. By regulating the polarity of the reaction system, temperature, and reaction time, various hierarchical structures, including cross-linked nanosheets, chestnut burr-like spheres, and starburst flower-like structures, are synthesized. The spiny projections and surface roughness endow the unique chestnut burr-like structure, achieving superior hydrophobicity and excellent microwave transmission properties. The formation of hierarchical structures is driven by intermolecular interactions during the nucleation and growth processes. The presence of both hydrophobic and hydrophilic domains within PANI particles leads to the coexistence of large water contact angles up to 152° and high surface energy. The optimized PANI structure minimizes the charge carrier mobility, dipole relaxation, and dielectric loss. A superior microwave transmission efficiency of up to 96% is achieved with these combined factors. By disclosing the relationship between the structure, wettability, and dielectric properties, a design protocol for the bionic regulation of micro-/nanostructures is established to achieve both superhydrophobic and excellent microwave-transparent functions.

2D WS2 monolayer preparation method and research progress in the field of optoelectronics.

Two-dimensional Transition Metal Dichalcogenides (2D TMDs) have garnered significant attention in the field of materials science due to their remarkable electronic and optoelectronic properties, including high carrier mobility and tunable band gaps. Despite the extensive research on various TMDs, there remains a notable gap in understanding the synthesis techniques and their implications for the practical application of monolayer tungsten disulfide (WS2) in optoelectronic devices. This gap is critical, as the successful integration of WS2 into commercial technologies hinges on the development of reliable synthesis methods that ensure high quality and uniformity of the material. In this study, we present a comprehensive overview of the synthesis techniques for monolayer WS2, focusing on mechanical stripping, Atomic Layer Deposition (ALD), and Chemical Vapor Deposition (CVD). We highlight the advantages of each method, such as the uniform growth achievable with ALD at low temperatures and the capability of CVD to produce large-area, high-quality monolayers. Additionally, we summarize the performance of WS2 in various electronic and optoelectronic applications, including field-effect transistors (FETs), photodetectors, and logic devices. Our findings indicate that with ongoing advancements in film uniformity, compatibility with existing semiconductor processes, and the long-term stability of WS2-based devices, there is a promising trajectory for the transition of 2D WS2 from laboratory research to practical applications. This work not only addresses the existing gaps in the literature but also underscores the potential of WS2 to significantly impact the future of optoelectronic technologies.&#xD.

Effective control of conductivity in lutetium orthoferrite with cobalt doping measured by terahertz time-domain spectroscopy

The effective control of conductivity in LuFeO3 (LFO) with Co3+ doping is explored by terahertz (THz) time-domain spectroscopy. It is demonstrated that the conductivity of 5% Co-doped LFO (LFO:Co 5%) is lower than that of LFO, while that of 15% Co-doped LFO (LFO:Co 15%) is significantly higher than LFO. Furthermore, LFO exhibits two lattice vibration peaks at 0.58 and 1.61 THz, LFO:Co 5% shows only one lattice vibration peak at 1.61 THz, while no distinct vibration peak is observed in LFO:Co 15%. The disappearance of lattice vibration at 0.58 THz is attributed to the shortened Fe (Co)-O bond length resulting from Co3+ doping, thus suppressing magnetic resonance effect of Fe3+. With 15% Co3+ doping, structural stability is enhanced, and the asymmetric vibration of Lu3+ at surface/interface/boundary is suppressed, resulting in the disappearance of vibration peak at 1.61 THz. The conductivity of LFO:Co 5% is lower than that of LFO, mainly because the lattice vibration at 1.61 THz and oxygen vacancy defects introduced by doping jointly increase the degree of carrier back-scattering, which decreases carrier movement, while the enhancement of conductivity by electronegativity at 5% Co3+ doping is very limited. The significantly higher conductivity of LFO:Co 15% compared to LFO is due to the obvious increase in overall electronegativity and suppression of lattice vibration by 15% Co3+ doping, thereby improving carrier mobility. The insights of this investigation provide important experimental data and theoretical basis for design and production of high-conductivity and stable solid oxide fuel cells cathode.

Advancing Thermoelectrics in Lead‐Free Rhombohedral GeTe via Interfacial Engineering With MXene

AbstractLead‐containing GeTe‐based thermoelectric (TE) materials exhibit outstanding performance, but the toxicity of lead (Pb) limits their practical applications. Lead‐free GeTe‐based TE materials present a promising alternative for environmentally sustainable and scalable applications. Here, Bi doping is used to reduce the majority carrier concentration in GeTe, combined with uniform incorporation of nanoscale layered MXene via high‐energy ball milling. This approach significantly enhances the structural symmetry of GeTe, while MXene further reduces carrier concentration and improves carrier mobility. Consequently, the Ge0.93Bi0.07Te‐0.6 mass% MXene sample achieves an impressive average power factor of ≈28.40 µW m−1 K−2 across 303–603 K. Moreover, point defects, multilayer nanostructures, and grain boundaries reduce thermal conductivity to ≈1.04 W m−1 K−1 at 603 K. A maximum ZTmax of ≈2.1 at 603 K, an average ZTavg of ≈1.1, and a Vickers microhardness of ≈ 236.75 Hv are obtained. In particular, a high power density of ≈1.54 W cm−2 and a maximum conversion efficiency of ≈7.5% at a temperature difference of 300 K are achieved in a 7‐pair TE module. These outcomes represent the highest performance levels for lead‐free GeTe‐based materials. This work uncovers a straightforward method to enhance the structural symmetry of GeTe‐based compounds, providing insights for advancing lead‐free TE technologies.