Improved Device Performance Research Articles

Accurate operando measurement of AlGaN/GaN HEMTs channel temperature and optimization of thermal design

The accurate estimation of the temperature distribution of the GaN based power devices and optimization of the device structure is of great significance to possibly solve the self-heating problem, which hinders the further enhancement of the device performances. We present here the operando temperature measurement with high spatial resolution using Raman spectroscopy of AlGaN/GaN high electron mobility transistors (HEMTs) with different device structures and explore the optimization of the device thermal design accordingly. The lateral and depth temperature distributions of the single-finger HEMT were characterized. The channel temperature and self-heating effect of the device under different bias voltages were investigated. By incorporating the two-dimensional electrothermal simulation, the hotspot position can be clearly observed under the gate edge near the drain side. The channel temperature of the multi-finger HEMT was further measured and the experiment results were in agreement with the three-dimensional finite element analysis simulation results. The device structure of the multi-finger device, including the gate width, gate pitch, structure layout, substrate materials, and thickness, were then theoretically optimized to improve the heat dissipation. The peak channel temperature of the device can be reduced by 70 °C when the substrate is substituted from silicon carbide to a single crystalline diamond. These results are of great interest for the thermal management of GaN HEMT power devices and further device performance improvement.

Complex thermoelectric transport in Bi-Sb alloys

Bi1−xSbx alloys are classic thermoelectric materials for near-cryogenic applications. Despite more than half a century of study, unraveling the underlying transport physics within this space has been nontrivial due to the complex electronic structure, disorder, and small bandgap within these alloys. Furthermore, as Peltier coolers, Bi1−xSbx alloys operate in a bipolar regime; as such, understanding the impact of minority carriers is critical for further improvements in device performance. This study unites first principles calculations with low-temperature experimental measurements to create a generalized model for transport within semiconducting Bi-Sb alloys. Our exploration reveals the interplay between the complex, degenerate valence band structure with the extremely light conduction bands. By building a hybrid computational/experimental model, an understanding of both the electron and hole relaxation times emerges both as a function of temperature and energy. Special quasi-random supercell calculations reveal that, despite significant atomic disorder, the electronic band structures within the alloy remains largely unaffected and electron–phonon scattering dominates. For charge carriers near the band edges, the relaxation times are thus extremely long, consistent with cyclotronic behavior appearing at low magnetic fields (≪ 1 T). Modeling thermoelectric performance suggests that the valence band edge deformation potential is significantly weaker and highlights the potential for p-type compositions to meet or exceed the current n-type alloys.

High‐Efficiency Solution‐Processed Organic Light‐Emitting Diodes Utilizing Multiple‐Resonance Emitters Incorporating Thiocarbazole Unit

AbstractIntroducing heavy atoms to enhance spin‐orbit coupling represents an effective strategy for boosting the reverse intersystem crossing (RISC) rate constants of Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters. Nevertheless, the restricted diversity of molecular structures obstructs a thorough investigation of structure‐property relationships, thereby limiting the improvement of device performance, especially in the case of solution‐processed devices. Herein, an alkylthio‐substituted carbazole building block is designed and developed two new MR‐TADF emitters, namely BNCz‐2S and BNCz‐4S. Quantum simulations and photophysical studies have revealed that as the number of sulfur atoms increases, BNCz‐4S exhibits a higher photoluminescence quantum yield (PLQY), a smaller singlet‐triplet energy gap (ΔEST) and reorganization energy, along with a larger spin‐orbit coupling (SOC) constant and a higher reverse intersystem crossing rate (kRISC) constants compared to BNCz‐2S. Consequently, solution‐processing devices based on BNCz‐4S exhibit a higher external quantum efficiency (EQE) of 24.06%, which is in the first tier of reported solution‐processed MR‐TADF organic light‐emitting diodes (OLED) to date.

Lyotropic Liquid Crystal Mediated Assembly of Donor Polymers Enhances Efficiency and Stability of Blade-Coated Organic Solar Cells.

Conjugated polymers can undergo complex, concentration-dependent self-assembly during solution processing, yet little is known about its impact on film morphology and device performance of organic solar cells. Herein, lyotropic liquid crystal (LLC) mediated assembly across multiple conjugated polymers is reported, which generally gives rise to improved device performance of blade-coated non-fullerene bulk heterojunction solar cells. Using D18 as a model system, the formation mechanism of LLC is unveiled employing solution X-ray scattering and microscopic imaging tools: D18 first aggregates into semicrystalline nanofibers, then assemble into achiral nematic LLC which goes through symmetry breaking to yield a chiral twist-bent LLC. The assembly pathway is driven by increasing solution concentration - a common driving force during evaporative assembly relevant to scalable manufacturing. This assembly pathway can be largely modulated by coating regimes to give 1) lyotropic liquid crystalline assembly in the evaporation regime and 2) random fiber aggregation pathway in the Landau-Levich regime. The chiral liquid crystalline assembly pathway resulted in films with crystallinity 2.63 times that of films from the random fiber aggregation pathway, significantly enhancing the T80 lifetime by 50-fold. The generality of LLC-mediated assembly and enhanced device performance is further validated using polythiophene and quinoxaline-based donor polymers.

Investigation of triple vertically stacked nanosheet FET with geometric variability at advanced technology node: DC, analog and RF performance benchmarking

Abstract This paper presents an in-depth analysis of the digital, analog, and radio frequency (RF) performance metrics of three-dimensional gate-all-around (GAA) triple nanosheet fieldeffect transistor (NSFET) designed for the 5 nm technology node. By optimizing the key physical dimensions of the NSFET specifically, a nanosheet width of 20 nm, thickness of 5 nm, and gate length of 12 nm, significant improvements in device performance were achieved. The optimized NSFET demonstrated a remarkable Ion/Ioff ratio of 2.99×10⁶, a low subthreshold swing of 65.63 mV/dec, and minimal drain-induced barrier lowering (DIBL) of 21.94 mV/V. Additionally, the device exhibited enhanced transconductance (gm = 3.2×10⁻⁴ S), contributing to a high intrinsic gain (Avo = 47 dB). In terms of RF performance, the NSFET achieved a cut-off frequency (fT) of 394 GHz and a maximum oscillation frequency (fmax) of 491 GHz, showcasing its potential for high-frequency applications. These results highlight the superior performance of NSFETs over FinFETs, making them a promising candidate for digital, analog, and RF circuit designs in advanced sub-5 nm technology nodes. The combination of excellent electrical characteristics and high-frequency performance positions NSFETs as a leading solution for next-generation integrated circuits.

High‐Performance and Ultrafast Single Germanium Nanowire Photodetectors

AbstractSemiconductor nanowire‐based photodetectors with high sensitivity and fast photoresponse in the near‐infrared wavelength range are crucial for applications in light‐wave communication switches, as well as environmental and atmospheric sensing. However, to advance this field, it is essential to develop innovative fabrication techniques that improve device performance. Here, the fabrication of an axial p–n junction along single germanium nanowires (Ge NWs) and their photoresponse characterization at near‐infrared wavelengths are reported. The resulting devices exhibit rectifying current–voltage characteristics with a high rectification ratio in dark conditions and operate with high sensitivity at zero bias under illumination. A high responsivity of 1.72 AW−1, a low noise‐equivalent power of 5.68 × 10−11 , and a high‐frequency response with a 3dB cut‐off frequency of 2.85 GHz are determined under 850 nm laser illumination at reverse bias. The high sensitivity of the Ge NW‐based photodetectors is ascribed to the radial built‐in electric field, which increases the carrier lifetime. In addition, the small size of the Ge NWs results in very small capacitance, leading to very fast response. These results have significant potential for advancing high‐speed and low‐power photodetectors in next‐generation optical communication systems and integrated optoelectronic devices.

Efficient defect passivation and charge extraction with 2-cyano-5-fluorobenzyl bromide interface modification for hole-transporting layers-free CsPbIXBr3−X perovskite solar cells

Abstract Fully inorganic metal halide perovskite solar cells (PSCs) have become an emerging research hotspot in photovoltaics due to their high efficiency and excellent thermal stability. Unfortunately, HTL-free CsPbIXBr3−X devices suffer from surface traps on the perovskite films, which severely limits the power conversion efficiency and operational stability of the devices. In this work, we propose a multifunctional passivator, 2-cyano-5-fluorobenzene bromide molecule (2-C-5-FB), to passivate perovskite films by post-treatment, aiming to improve the quality of perovskite films, reduce interfacial defects and non-radiative complexes, enhance carrier separation kinetics, and improve the extraction of carriers, thus improving device performance. The C≡N in the molecular structure immobilizes the undercoordinated Pb2+ ions, thus passivating the defects in the perovskite films. In addition, the Br atoms on the ring can with the [PbI6]4− backbone through halogen bonding, and the F atoms form Pb-F and Cs-F, which can effectively reduce the film defects. We prepared passivated devices with the structure of FTO/TiO2/CsPbIXBr3−X/2-C-5-FB/Carbon, and the PCE of the passivated devices was improved compared with the pristine devices, and the cell efficiency was increased from 7.84% to 9.21% with a light intensity of 100 mW cm−2, and the stability of the devices was also improved. The experimental results indicate that the use of 2-cyano-5-fluorobenzene bromide passivation strategy has a positive effect on the performance enhancement of the perovskite devices, and is an effective way to realize efficient and stable PSCs.

Effect of Fabricating Process on the Performance of Two-Dimensional p-Type WSe2 Field Effect Transistors.

Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as WSe2, are promising candidates for next-generation integrated circuits. However, the dependence of intrinsic properties of TMD devices on various processing steps remains largely unexplored. Here, using pristine p-type WSe2 devices as references, we comprehensively studied the influence of each step in traditional nanofabrication methods on device performance. Our findings reveal that electron beam exposure significantly alters the electrical conductivity of WSe2 due to the doping and diffusion effects of electrons. During ultraviolet lithography, the bilayer WSe2 device immersed in a 4‰ NaOH developer also showed substantial quality degradation (40%-84%). In this case, we combined laser patterning with the transfer electrode method to fabricate a high-performance device with a current density of 278.5 μA/μm and an on/off ratio of 3.9 × 107. This work reveals the influence of the nanofabrication process on TMD devices and guides for improving device performance.

Significant Efficiency Enhancements in Non-Y Series Acceptors by the Addition of Outer Side Chains.

Most current highly efficient organic solar cells utilize small molecules like Y6 and its derivatives as electron acceptors in the photoactive layer. In this work, a small molecule acceptor, SC8-IT4F, is developed through outer side chain engineering on the terminal thiophene of a conjugated 6,12-dihydro-dithienoindeno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IDTT) central core. Compared to the reference molecule C8-IT4F, which lacks outer side chains, SC8-IT4F displays notable differences in molecule geometry (as shown by simulations), thermal behavior, single-crystal packing, and film morphology. Blend films of SC8-IT4F and the polymer donor PM6 exhibit larger carrier mobilities, longer carrier lifetimes, and reduced recombination compared to C8-IT4F, resulting in improved device performance. Binary photovoltaic devices based on the PM6:SC8-IT4F films reveal an optimal efficiency over 15%, which is one of the best values for non-Y type small molecule acceptors (SMAs). The resultant devices also show better thermal and operational stability than the control PM6:L8-BO devices. SC8-IT4F and its blend exhibit a higher relative degree of crystallinity and π coherence length, compared to C8-IT4F samples, beneficial for charge transport and device performance. The results indicate that outer side chain engineering on existing small electron acceptors can be a promising molecular design strategy for further pursuing high-performance organic solar cells.

Interfacial Elemental Analysis of Slanted Edge-Contacted Monolayer MoS2 Transistors via Directionally Angled Etching.

Edge contacts offer a significant advantage for enhancing the performance of semiconducting transition metal dichalcogenide (TMDC) devices by interfacing with the metallic contacts on the lateral side, which allows the encapsulation of all of the channel material. However, despite intense research, the fabrication of feasible electrical edge contacts to TMDCs to improve device performance remains a great challenge, as interfacial chemical characterization via conventional methods is lacking. A major bottleneck in explicitly understanding the chemical and electronic properties of the edge contact at the metal-two-dimensional (2D) semiconductor interface is the small cross section when characterizing nominally one-dimensional edge contacts. Here, we demonstrate a directional angled etching technique that enables the characterization of the interfacial chemistry at the metal-MoS2 junction when in an edge-contact configuration. The slanted edge structure provides a substantial cross section for elemental analysis of the edge contact by conventional X-ray photoemission spectroscopy, in which a simple chemical environment and sharp interface were revealed. Facilitated by the well-characterized contact interface, we realized slanted edge-contacted monolayer MoS2 transistors encapsulated by hexagonal boron nitride. The transport characteristics and photoluminescence of these transistors allowed us to attribute the efficient carrier injection to direct and Fowler-Nordheim tunneling, validating the distinct Au-MoS2 interface. The established method represents a viable approach to fabricating edge contacts with encapsulated 2D material devices, which is crucial for both the fundamental study of 2D materials and high-performance electronic applications.

Recent Progress and Advances of Perovskite Crystallization in Carbon-Based Printable Mesoscopic Solar Cells.

Carbon-based printable mesoscopic solar cells (p-MPSCs) offer significant advantages for industrialization due to their simple fabrication process, low cost, and scalability. Recently, the certified power conversion efficiency of p-MPSCs has exceeded 22%, drawing considerable attention from the community. However, the key challenge in improving device performance is achieving uniform and high-quality perovskite crystallization within the mesoporous structure. This review highlights recent advancements in perovskite crystallization for p-MPSCs, with an emphasis on controlling crystallization kinetics and regulating perovskite morphology within confined mesopores. It first introduces the p-MPSCs, offering a solid foundation for understanding their behavior. Additionally, the review summarizes the mechanisms of crystal nucleation and growth, explaining how these processes influence the quality and performance of perovskites. Furthermore, commonly applied strategies for enhancing crystallization quality, such as additive engineering, solvent engineering, evaporation controlling, and post-treatment techniques, are also explored. Finally, the review proposes several potential suggestions aimed at further refining perovskite crystallization, inspiring continued innovation to address current limitations and advance the development of p-MPSCs.

Improved Device Performance and Stability of Less Toxic Solvent-Processed Perovskite Solar Cells with Self-Assembled Molecules

Improved Device Performance and Stability of Less Toxic Solvent-Processed Perovskite Solar Cells with Self-Assembled Molecules

Application of Photolithography in Integrated Circuits

Integrated circuit (IC) manufacturing relies heavily on lithography, which drives device size reduction and performance improvement through precise pattern transfer. As the performance requirements of electronic devices continue to increase, lithography faces major challenges in terms of precision and efficiency. Currently, deep ultraviolet (DUV) and extreme ultraviolet (EUV) lithography technologies are mainstream, while technologies such as electron beam lithography (EBL) and directed self-assembly (DSA) are applied in specific high-precision fields. This paper reviews the current development status of lithography technology and analyzes its application in CMOS technology, 3D NAND flash memory, and high-performance computing components. The study also explores the main challenges facing photolithography, including technical bottlenecks, rising costs, and environmental impacts. In order to address these issues, the study emphasizes the importance of technological innovation and material improvement, especially in the development of new photoresists and mask materials and the promotion of environmentally friendly lithography technology. Therefore, it can be found that continued advances in lithography are essential to meet the changing needs of the semiconductor industry.

Development and Validation of a Capacitor–Current Circuit Model for Evaporation-Induced Electricity

Evaporation-induced electricity is a promising approach for sustainable energy generation which is particularly suited for off-grid and Internet-of-Things (IoT) applications. Despite significant progress, the mechanism of electricity generation remains debated due to complex factors. In this study, we introduce a simplified capacitor–current circuit model to describe the behavior of evaporation-induced electricity. The primary objective of this work is to provide a framework for understanding the transient and steady-state behavior of this phenomenon. We validated this model using experimental data from wood-based nanogenerators with citric acid modified microchannels. The fitting results revealed a steady-state current of approximately 9.832 μA and an initial peak current of 16.168 μA with a time constant of 621.395 s. These findings were explained by a hybrid model incorporating a capacitor and current source components, and subsequent discharge through internal resistance. This simplified model paves the way for better understanding and optimization of evaporation-induced electricity, highlighting potential improvements in device design for enhanced performance. While improving device performance is beyond the scope of this study, the insights gained from this model offer a foundation for future optimization and the enhanced performance of evaporation-induced electricity generation devices.

Stable Halide Perovskite Memristor Utilizing Innovative Silver/Bismuth Electrode as an Alternative to Gold

AbstractPerovskite memristors hold great promise for neuromorphic computing due to their ease of fabrication and sensitivity to light and electrical stimuli. However, the common use of expensive metal electrodes, such as gold (Au) and unstable silver (Ag), limits their stability and broader application. In this study, a cost‐effective perovskite memristor utilizing a novel Ag/Bismuth (Ag/Bi) bilayer electrode, which serves as a viable alternative to Au while maintaining excellent performance, is presented. This design prevents electrochemical reactions and the formation of unstable metallic filaments, enabling controlled mixed electronic/ionic conductivity. Moreover, the low work function of the Ag/Bi bilayer reduces the built‐in voltage, facilitating the formation and retention of conductive filaments, which improves device performance and stability. The memristor exhibits a high on/off ratio (102), excellent endurance (≈800 cycles), long retention (>104 s), and storage stability comparable to Au‐based devices. Furthermore, it demonstrates neuromorphic synaptic behaviors, including long‐ and short‐term plasticity (STP), potentiation/depression, and spike‐timing‐dependent plasticity (STDP). When integrated into a spiking neural network (SNN) for digital image recognition using the MNIST dataset, the device achieves an accuracy of 86.68%. This work demonstrates the potential of the cost‐effective Ag/Bi bilayer electrode in enhancing the stability and performance of perovskite memristors.

Selenium Interface Layers Boost High Mobility and Switch Ratios in van der Waals Electronics.

Achieving high mobility while minimizing off-current and static power consumption is critical for applications of two-dimensional field-effect transistors. Herein, a selenium (Se) sacrificial layer is introduced between the rhenium sulfide (ReS2) semiconductor and source/drain electrode. With the Se layer and postannealing process, the ReS2 transistor significantly decreases the off-state current with a substantial increase in the on-state current density. Notably, the mobility reaches 237 cm2 V-1 s-1, which is accompanied by an extraordinary current on/off ratio of 1011 at 7 K. The theoretical calculations and noise analysis show that the improvement in device performance is ascribed to the Se protective layer, which effectively shields the semiconductor from direct exposure to high-energy metal particles, reducing the Schottky barrier and the number of defect states at the interface. Finally, Se sacrificial ReS2 transistor-based versatile logic circuits including NAND and NOR logic are executed, which can be widely applied in integrated circuits.

Extending Exciton Diffusion Length via an Organic‐Metal Platinum Complex Additive for High‐Performance Thick‐Film Organic Solar Cells

AbstractThe long exciton diffusion length (LD) plays an important role in promoting exciton dissociation, suppressing charge recombination, and improving the charge transport process, thereby improving the performance of organic solar cells (OSCs), especially in thick‐film OSCs. However, the limited LD hinders further improvement in device performance as the film thickness increases. Here, an organic‐metal platinum complex, namely TTz‐Pt, is synthesized and served as a solid additive into the D18‐Cl:L8‐BO system. The addition of TTz‐Pt enhanced the crystallinity of blends, reduced energy disorder, and trap density, and decreased non‐radiative recombination and exciton binding energy, which is conducive to prolonging the LD in the TTz‐Pt‐treated film, thereby facilitating the exciton dissociation and charge transport process along with inhibiting the charge recombination. Consequently, the TTz‐Pt‐treated D18:L8‐BO:IDIC device (100 nm) exhibits a champion power conversion efficiency (PCE) of 20.12% (certified as 19.54%), one of the highest PCEs reported for OSCs to date. Remarkably, a record‐breaking PCE of 18.84% is yielded for the active layer thickness of 300 nm. Furthermore, the TTz‐Pt exhibits superior universality in improving the performance of OSCs. This work provides a simple and universal approach to extending LD by introducing an organic‐metal platinum complex as a solid additive to achieve highly efficient thick‐film OSCs.

Unlocking the solar potential: elevating open circuit voltage in kesterite CZTS thin film solar cells through cutting-edge SCAPS modeling

Abstract Kesterite-based CZTS thin-film solar cells are gaining recognition as a sustainable alternative to traditional photovoltaic technologies that rely on environmentally hazardous and costly absorber materials like c-Si, CdTe, and CIGS. The United Nations Sustainable Development Goals (UNSDGs) 7 (Affordable and Clean Energy) and 13 (Climate Action) are particularly relevant to CZTS technology. However, the efficiency of CZTS solar cells is currently constrained by the relatively low open circuit voltage (Voc), which remains a primary barrier to their widespread adoption. This study uses cutting-edge SCAPS modeling to identify and address CZTS solar cell Voc constraints. The study optimizes acceptor, donor, and neutral defect states, shunt resistance, and interface states to improve device performance. Optimizing these parameters improves Voc and power conversion efficiency using rigorous numerical simulations. By optimizing defect states, the proposed MoS2/CZTS/CdS/ZnO structure achieved an improved open-circuit voltage (Voc) of up to 1.10 V and an efficiency of up to 18.61%. This work makes solar energy more accessible and inexpensive by enhancing CZTS solar cell efficiency, especially in locations where conventional photovoltaic technologies are less practical due to economic or environmental constraints.

Efficient Narrow Bandgap Pb‐Sn Perovskite Solar Cells Through Self‐Assembled Hole Transport Layer with Ionic Head

AbstractSingle‐junction perovskite solar cells (PSCs) have achieved certified power conversion efficiencies (PCEs) of 26.1%, which approaches their practical performance limit. Multi‐junction tandem solar cells can unlock even higher PCEs, where narrow‐bandgap lead‐tin (Pb‐Sn) perovskites, with a bandgap of 1.21–1.25 eV, are well‐suited as the bottom photo absorber in all‐perovskite tandems. Bulk engineering and surface treatments of Pb‐Sn perovskites using Lewis base molecules have been shown to reduce the defect density within the bulk and at the electron transport layer interface, thereby improving device performance. Nevertheless, the buried interface between Pb‐Sn perovskite and the commonly used hole transport layer PEDOT:PSS remains problematic due to the reactivity of polystyrene sulfonate (PSS) with Sn2+ ions, which negatively impacts device performance. To overcome this issue, a novel carbazole‐based self‐assembled monolayer, BrNH3‐4PACz is synthesized, that provides a suitable dipole moment at the indium‐tin oxide interface for efficient hole extraction and features an ionic ammonium head group that passivates the perovskite at the buried interface. This dual functionality enabled the fabrication of a p‐i‐n architecture Pb‐Sn PSC with a bandgap of 1.24 eV, achieving a champion PCE of 23% and an open‐circuit voltage of 0.88 V, which ranks among the highest reported values in the literature.

Femtosecond laser induced ultrafast interface dynamics between single layer graphene and quartz substrate: A theoretical study

SiO2 is the most widely used dielectric substrate for graphene devices. Theoretically investigating the interaction between graphene and SiO2 is vitally important for understanding graphene properties and improving device performance. In recent years, density functional theory (DFT) has been used to investigate the graphene–SiO2 interaction in ground states. However, the strong interface dynamics for an excited graphene–SiO2 system in ultrafast nonequilibrium processes was rarely researched. In this work, a real-time time-dependent density functional theory (rt-TDDFT) method was adopted to study the femtosecond laser induced ultrafast structure evolution and the underlying dynamics mechanism of the interface between a single layer graphene and a Si-terminated quartz substrate. This work indicates that rt-TDDFT is a promising method to study the strong electron dynamics and the coupled nuclear dynamics for graphene-SiO2 interfaces under ultrafast optical excitation, which benefits graphene device designs and mechanism analysis.