Enhanced Device Performance Research Articles

Challenges and advancements in p-GaN gate based high electron mobility transistors (HEMTs) on silicon substrates

This review highlights the challenges and advancements in p-GaN gate HEMTs on silicon substrates. It also discusses several attempts to enhance device performance and explores the future developments of p-GaN gate HEMT.

CuO nanostructure-decorated InGaN nanorods for selective H2S gas detection.

Establishing a heterostructure is one of the adequate strategies for enhancing device performance and has been explored in sensing, and energy applications. In this study, we constructed a heterostructure through a two-step process involving hydrothermal synthesis of CuO nanostructures and subsequent spin coating on MBE-grown InGaN NRs. We found that the CuO content on the InGaN NRs has a great impact on carrier injection at the heterojunction and thus the H2S gas sensing performance. Popcorn CuO/InGaN NR shows excellent gas sensing performance towards different concentrations of H2S at room temperature. The highest response is up to 35.54% to a H2S concentration of 100 ppm. Even more significantly, this response is further enhanced significantly (123.70%) under 365 nm UV light. In contrast, this composite structure exhibits negligibly low responses to 100 ppm of NO2, H2, CO, and NH3. The heterostructure band model associated with a surface reaction model is manifested to elucidate the sensing mechanism.

Fine-tuning of film morphology through addition of a third component enables organic solar cells with efficiency over 18%

By incorporating an acceptor Y-TNF with a structure analogous to Y6 as the third component, the nanofiber structure of the active layer is further optimized, the molecular arrangement is more ordered, and the PCE of the device reaches 18.1%.

Analytical modelling of the transport in analog filamentary conductive-metal-oxide/HfOx ReRAM devices.

The recent co-optimization of memristive technologies and programming algorithms enabled neural networks training with in-memory computing systems. In this context, novel analog filamentary conductive-metal-oxide (CMO)/HfOx redox-based resistive switching memory (ReRAM) represents a key technology. Despite device performance enhancements reported in literature, the underlying mechanism behind resistive switching is not fully understood. This work presents the first physics-based analytical model of the current transport and of the resistive switching in these devices. As a case study, analog TaOx/HfOx ReRAM devices are considered. The current transport is explained by a trap-to-trap tunneling process, and the resistive switching by a modulation of the defect density within the sub-band of the TaOx that behaves as electric field and temperature confinement layer. The local temperature and electric field distributions are derived from the solution of the electric and heat transport equations in a 3D finite element ReRAM model. The intermediate resistive states are described as a gradual modulation of the TaOx defect density, which results in a variation of its electrical conductivity. The drift-dynamics of ions during the resistive switching is analytically described, allowing the estimation of defect migration energies in the TaOx layer. Moreover, the role of the electro-thermal properties of the CMO layer is unveiled. The proposed analytical model accurately describes the experimental switching characteristic of analog TaOx/HfOx ReRAM devices, increasing the physical understanding and providing the equations necessary for circuit simulations incorporating this technology.

Enhancing performance and scalability of HTL-free organic solar cells with keggin polyoxometalates-type additive

Interfacial layers play a crucial role in enhancing the performances and stabilities of organic solar cells (OSCs). Despite achieving high efficiencies from OSCs, the challenges associated with large-area manufacturing and the need for nanoscale uniformity during coating have hindered the large-scale production of these devices. To address these issues, we propose the concept of hole transport layer (HTL)-free OSCs to simplify the fabrication processes and improve the efficiency of production. In this study, we explore the potential of phosphotungstic acid (PTA), a Keggin polyoxometalate, both as a promising HTL and as an additive in HTL-free OSCs to enhance device performances and scalabilities in cell-to-module OSCs. Remarkably, incorporating PTA as an annealing-free HTL and as an additive in the photoactive layer (PM6:Y6:PC71BM) significantly increases power conversion efficiency (PCE) up to 17.28 % and 16.33 %, respectively, with respect to that of the reference device with PEDOT:PSS (15.88 %). We successfully fabricate a large-area OSC module, exhibiting an impressive PCE of 15.18 % and an active area of 54 cm2, achieving approximately 85 % of the effectiveness of small-area OSCs. The improved performance is attributed to the enhanced transmittance, excellent carrier-dynamic capacity, suppressed carrier recombination, and reduced trap-states in the ternary bulk-heterojunction OSCs. This study demonstrates the promising versatility of PTA for application in OSCs, offering potential enhancements in device performance and scalability for future applications.

Tailoring hole-selective contacts via self-assembled monolayers for advancing indoor organic photovoltaic and capacitor devices

Amidst the growing demand for transparent devices, the current research is centered on the advancement of technologies involving self-assembled monolayer (SAM)-treated transparent conductive electrodes. However, the detailed mechanisms governing surface energy reactions in these devices at the molecular scale remain unclear, underscoring the need for additional investigations. This study explored the effect of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) derivatives (MeO-2PACz, 2PACz, Br-2PACz) with a carbazole core on the properties of indium tin oxide (ITO) electrodes. On adsorbing 2PACz molecules onto the ITO surfaces, interfacial dipoles formed through chemisorption between the phosphonic acid oxygen and indium atoms, elevating the work function (WF). 2PACz treatment enhanced the electronic properties of the electrodes for indoor organic photovoltaics (OPV) and metal–insulator-metal (MIM)-capacitors.. The optimized Br-2PACz-based indoor OPVs achieved a remarkable 31.0 % power conversion efficiency and an excellent fill factor of 78.0 % under LED 1000 lx conditions. Furthermore, Br-2PACz-based MIM-capacitors exhibited a reduction in leakage current greater than 19,000 times compared to that of the TiN-electrode-based MIM-capacitors. These outstanding electronic device achievements were attributed to the elevated WFs of the electrodes achieved through the 2PACz treatment. This research underscores the manifold enhancements in device performance achieved through refined energy-level alignment stemming from the increased WFs facilitated by SAM integration.

Enhancement of NbO2-based oscillator neuron device performance via cryogenic operation

The Niobium Dioxide (NbO2) oscillator neuron has garnered significant interest because of its simple structure compared to conventional CMOS-based circuits. However, the limited on/off resistance ratio narrows the range of series resistances that satisfy the self-oscillation conditions and limits its use in large-scale synaptic arrays. In this study, we report the possibility of improving the performance of NbO2-based oscillator neuron devices through cryogenic operation. The study emphasizes two crucial parameters: the on/off resistance ratio and the oscillation amplitude, both of which are essential for accurate weighted sum classification. The data suggest that these parameters can be effectively enhanced under cryogenic conditions. In addition, we revealed that 120 K is the optimal temperature for cryogenic operation, as it represents the temperature where the on/off resistance ratio ceases to increase. As a result, we revealed that the series resistance range satisfying the self-oscillation condition in a single oscillator increases from 20 to 126 kΩ. The research also probes the maximum possible array size at each temperature. At 300 K, representation is only possible for a 5 × 5 array, but at 120 K, a 30 × 30 array can be represented as a frequency. The evidence implies that the 120 K conditions not only broaden the range of series resistors that can be connected to a single oscillator but also increases the array size, thereby representing different weighted sum currents as frequencies. The research indicates that using carefully optimized cryogenic operation could be a viable method to enhance the necessary NbO2 properties for an oscillator neuron device.

High Performance Sub-10nm Si-doped MoS2 based Step Structure DG-TFET

Two-dimensional (2D) nanomaterials, which include Molybdenum Disulfide (MoS2), are the focus research because of the wide possibilities of application in electronic and optoelectronic devices. Nanomaterials have potential use in high-performance transistors. The main objective of this study is to examine and evaluate a Silicon (Si)-doped MoS2 Step Structured Tunnel Field Effect Transistor (MoS2-SS-TFET). The energy gap in MoS2 is controlled by is controlled by thickness engineering, this unique property is used to design a device. At the source side and drain side of the channel, three layers and one layer of Si-doped MoS2 are used to build the step structure in order to increase the on-state current. The Subthreshold Swing (SS), threshold voltage (Vth), on-current (Ion), and off-current (Ioff) performance parameters for the device have been computed. In comparison of the study with other simulated devices, the Si-doped MoS2-SS-TFET has demonstrated enhanced device performance metrics. The device attributes such as work-function of dual metal, channel length ratio of proposed device, dielectric material and oxide thickness scaling are optimized for the improved device design.

Fabrication and structure analysis of freestanding BaTiO3–CeO2 epitaxial nanocomposite membranes

Vertically aligned nanocomposite films hold the promise of making a significant contribution to the performance enhancement and multifunctional integration of flexible thin-film devices but are hindered by the difficulty of direct epitaxial growth on flexible substrates. In this work, freestanding BaTiO3–CeO2 epitaxial nanocomposite membranes were prepared by using water-soluble Sr3Al2O6 as the sacrificial buffer during film deposition. The membrane's lattice parameters as well as their epitaxial relationship, before and after its removal from the single-crystal substrates, were quantitatively measured and analyzed by combining x-ray diffraction and TEM. In addition, synchrotron soft x-ray absorption spectroscopy reveals the discrepancy in the surface and internal electron states of Ce and Ti via comparative studies in total electron yield mode and transmission mode, respectively. This work exemplified that freestanding membranes provide a convenient platform for (1) the study of in-plane lattice information of epitaxial oxide films via TEM and for (2) the comparative study of surface and internal electron band information of epitaxial oxide films.

Performance enhancement of blue organic light-emitting devices by inserting BPhen: Alq3 as an n-doping electron transport layer

An n-doping electron transport layer (ETL) that consists of 4-7-diphenyl-1, 10-phenanlhroline (BPhen) and tris(8-hydroxyquinoline) aluminum (Alq3) was applied to enhance the performance of blue organic light-emitting diodes (OLEDs). The resulting n-doping OLED afforded a maximum luminance efficiency of 8.24 cd/A, which was higher than the devices using either BPhen or Alq3 as ETL by 56.9 % and 91.2 %, respectively. In addition, this device was found to possess a higher maximum power efficiency of 5.17 Lm/W compared to the blue OLEDs without such n-doping ETL concentrations. By performing the hole- and electron- ‘only’ devices and the density functional theory (DFT) calculations, we show that the enhancement of the device performance can be attributed to increased electron injection/transport at ETL interfaces and hence improved carrier balance in emission layer (EML).

Large Deflection and Post-Buckling Analysis of Cantilever Nanorods Including Effects of Couple and Surface Stresses by Intrinsic Coordinate Finite Elements

This paper presents a novel approach to the analysis of large deflection and post-buckling behavior of cantilever nanorods under different load conditions. The proposed approach utilizes a variational method, incorporating the Gurtin–Murdoch surface elasticity theory and the consistent couple stress theory to account for size-dependency effects. By accounting for the strain energy contributions of the bulk material, surface layer, and load conditions, this approach expresses the behavior of the nanorods in terms of their intrinsic coordinates. A finite element method was used to solve this numerical problem, generating a system of non-linear equations that were iteratively solved using the Newton–Raphson method. The results obtained from the finite element method were confirmed by those from the shooting method. Also, it highlights the effectiveness of the variational model in predicting the large deflection and post-buckling behavior of cantilever nanorods while considering both surface stress and couple stress effects. Furthermore, the study investigated the influence of surface stress and couple stress on the response of the nanorods to point and uniform loads. The results showed that incorporating both effects enhanced the stiffness of the nanorods compared to scenarios in which these effects were neglected. In addition, the couple stress effect was found to have a greater influence on the stiffening of nanorods for the same value of unitless parameters compared to surface stress effects. These findings offer valuable insights into the large deflection and post-buckling behavior of cantilever nanorods and highlight the importance of surface stress and couple stress effects. The model proposed in this study has potential applications in advanced technological device designs by providing a comprehensive understanding of the mechanical response of nanorods, allowing for more accurate predictions and enhanced device performance.

Enhancing microstructure and device performance of InGaN quantum dot micro-LEDs through substrate off-cut angle modulation

InGaN quantum dots (QDs) are regarded as a compelling candidate material for the fabrication of high-quality GaN-based micro-LEDs. In this work, to study the impact of a substrate structure on InGaN QDs and QD-based micro-LEDs, GaN-on-sapphire substrates with off-cut angles toward the a-axis of 0.2°, 0.4°, and 0.7° were utilized as templates for the fabrication of InGaN QDs and InGaN QDs-based micro-LEDs. Experimental results show that GaN template with 0.4° off-cut angle exhibits the narrowest terrace width and enables InGaN QDs to be higher and more uniform. The InGaN QD sample grown on 0.4° substrate has a very small wavelength shift of 2.5 nm with temperature increasing and owns the longest photoluminescence peak wavelength implying the highest In content. Furthermore, electroluminescence (EL) spectra demonstrate that QD-based micro-LED array has excellent wavelength stability under various injection currents, and the stability can be improved further on a GaN template with narrower terraces. The results indicate that altering the terrace width of GaN template is a feasible scheme for improving the properties of GaN-based micro-LEDs.

Understanding the Heterointerfaces in Perovskite Solar Cells via Hole Selective Layer Surface Functionalization.

Interfaces in perovskite solar cells (PSCs) play a pivotal role in determining device performance by influencing charge transport and recombination. Understanding the physical processes at these interfaces is essential for achieving high-power conversion efficiency in PSCs. Particularly, the interfaces involving oxide-based transport layers are susceptible to defects like dangling bonds, excess oxygen, or oxygen deficiency. To address this issue, the surface of NiOx is passivated using octadecylphosphonic acid (ODPA), resulting in improved charge transport across the perovskite hole transport layer (HTL) interface. This surface treatment has led to the development of hysteresis-free devices with an impressive ≈13% increase in power conversion efficiency. Computational studies have explored the halide perovskite architecture of ODPA-treated HTL/Perovskite, aiming to unlock superior photovoltaic performance. The ODPA surface functionalization has demonstrated enhanced device performance, characterized by superior charge exchange capacity. Moreover, higher band-to-band recombination in photoluminescence and electroluminescence indicates presence of lower mid-gap energy states, thereby increasing the effective photogenerated carrier density. These findings are expected to promote the utilization of various phosphonic acid-based self-assembly monolayers for surface passivation of oxide-based transport layers in perovskite solar cells. Ultimately, this research contributes to the realization of efficient halide PSCs by harnessing the favorable architecture of NiOx interfaces.

High-Quality Hybrid Perovskite Thin Films by Post-Treatment Technologies in Photovoltaic Applications.

Incredible progress in photovoltaic devices based on hybrid perovskite materials has been made in the past few decades, and a record-certified power conversion efficiency (PCE) of over 26% has been achieved in single-junction perovskite solar cells (PSCs). In the fabrication of high-efficiency PSCs, the postprocessing procedures toward perovskites are essential for designing high-quality perovskite thin films; developing efficient and reliable post-treatment techniques is very important to promote the progress of PSCs. Here, recent post-treatment technological reforms toward perovskite thin films are summarized, and the principal functions of the post-treatment strategies on the design of high-quality perovskite films have been thoroughly analyzed by dividing into two categories in this review: thermal annealing (TA)-related technique and TA-free technique. The latest research progress of the above two types of post-treatment techniques is summarized and discussed, focusing on the optimization of postprocessing conditions, the regulation of perovskite qualities, and the enhancement of device performance. Finally, an outlook of the prospect trends and future challenges for the fabrication of the perovskite layer and the production of highly efficient PSCs is given.

Significant dark current suppression in perovskite photodetectors using hole transport materials of lithium-doped vanadium oxide

Suppressing dark current density (Jdark) is one of most important strategies for improving responsivity (R), detectivity (D*), and linear dynamic rang (LDR) of perovskite photodetectors (PDs). However, the modulation mechanism of intrinsic and interfacial features of hole transport materials (HTMs) on their photodetection performance remains unclear and is related to complicated factors, resulting in perovskite PDs to generally suffer from high Jdark. In this study, we systematically investigated the effect of Li-doped VOX on the photodetection performance of perovskite PDs. The Li-doped VOX HTMs showed superior conductivity, high transmittance, and enlarged interfacial adhesion between the HTMs and perovskite layer. The PDs based on Li-doped VOX HTMs exhibited at least two orders lower Jdark and almost 1.6 times greater photocurrent densities (Jph) compared with those based on pristine VOX HTMs, while significantly maintained high external quantum efficiency (∼84 %) and impressive Dmax* of 1.23 × 1013 Jones. The enlarged surface roughness of Li-doped VOX HTMs leads to the enhancement of the interfacial adhesion between the HTMs and perovskite layer, which decreases the defects density of perovskite layer and trap-assisted recombination inside PDs, thus resulting in the significant suppression of Jdark and the improved collection of photoinduced charges. Overall, our findings provide a facial way to suppress Jdark for enhancing device performance of PDs.

Electrical performance estimation and comparative study of heterojunction strained and conventional gate all around nanosheet field effect transistors

Abstract In this paper, we propose a novel type of Gate All Around Nanosheet Field Effect Transistor (GAA NS FET) that incorporates source heterojunctions and strained channels and substrate. We compare its electrical characteristics with those of the Heterojunction Gate All Around Nanosheet Field Effect Transistor (Heterojunction GAA NS FET) and the Conventional Gate All Around Nanosheet Field Effect Transistor (Conventional GAA NS FET). We investigate the impact of electrostatic control on both DC and analog parameters such as gate capacitance (C gg), transconductance g m, and cut-off frequency (f T) for all three device types. In our Proposed GAA NS FET, we employ Germanium for the source and substrate regions, Silicon/Germanium/Silicon (Si/Ge/Si) for the channel, and Silicon for the drain region. The introduction of strain into the nanosheet and the use of a heterojunction structure significantly enhance device performance. Before utilizing a model to analyze a semiconductor device, it is crucial to accurately determine and elaborate on the model parameters. In this case, we solve the Density Gradient (DG) equation self-consistently to obtain the electrostatic potential for a given electron Fermi-level distribution, use the Shockley-Read-Hall (SRH) equation to estimate carrier generation, account for bandgap narrowing in transport behavior, and consider auger recombination. Our general results indicate a notable improvement in drain current, transconductance, and unity-gain frequency by approximately 42%, 53%, and 31%, respectively. This enhancement results in superior RF performance for the Proposed GAA NS FET compared to both the heterojunction GAA NS FET and the conventional GAA NS FET.

Reduction of phosphorus diffusion in bulk germanium via argon/phosphorus co-implantation and RTA annealing

Germanium has received increased research interest for use in next-generation CMOS technology as its high carrier mobilities allow for enhanced device performance without further device scaling. Fabrication of high-performance NMOS Ge devices is hindered by high diffusivity and low activation of n-type implanted dopants. While the high solid solubility of P in Ge makes it an ideal dopant, its diffusion mechanism is poorly understood and results in heavy tradeoffs between implanted dopant diffusion and electrical activation. In this study, we demonstrate the suppression of in-diffusion of implanted P via a co-implantation with Ar. Diffusivity of implanted P species and their activation is investigated over a wide range of annealing temperatures and times. P diffusion was explored by secondary-ion-mass-spectrometry and the diffusivity of P was extracted by solving the 2D diffusion equation using the Crank–Nicolson method, and the dopant electrical activation was extracted from the Hall effect measurements. The co-implantation of P with Ar entirely suppresses P in-diffusion up to annealing temperatures as high as 700 °C but at the cost of its reduced electrical activation. Extracted diffusivity reveals a highly correlated exponential relationship with annealing. P activation energy was extracted from Arrhenius behavior. A 450 °C/10 min annealing of P implant shows negligible in-diffusion of P with the activation as high as 70%. RTA processing of the Ar/P co-implanted sample at 750 °C for 1 min results in a negligible P in-diffusion and an electrical activation of 20%.

Recent Progress of Vertical Graphene: Preparation, Structure Engineering, and Emerging Energy Applications.

Vertical graphene (VG) nanosheets have garnered significant attention in the field of electrochemical energy applications, such as supercapacitors, electro-catalysis, and metal-ion batteries. The distinctive structures of VG, including vertically oriented morphology, exposed, and extended edges, and separated few-layer graphene nanosheets, have endowed VG with superior electrode reaction kinetics and mass/electron transportation compared to other graphene-based nanostructures. Therefore, gaining insight into the structure-activity relationship of VG and VG-based materials is crucial for enhancing device performance and expanding their applications in the energy field. In this review, the authors first summarize the fabrication methods of VG structures, including solution-based, and vacuum-based techniques. The study then focuses on structural modulations through plasma-enhanced chemical vapor deposition (PECVD) to tailor defects and morphology, aiming to obtain desirable architectures. Additionally, a comprehensive overview of the applications of VG and VG-based hybrids d in the energy field is provided, considering the arrangement and optimization of their structures. Finally, the challenges and future prospects of VG-based energy-related applications are discussed.

A breakthrough for temperature and linearity stability from device to circuit-level with 14 nm junctionless SOI FinFET: Advancing K-band LNA performance

SOI junctionless (JL) FinFETs are well-suited for future wireless communication systems; however, they suffer from the self-heating effect (SHE), which diminishes performance at higher temperatures. We proposed a novel structure called p-layer JL-FinFET (pL-JL-FinFET) to improve high-frequency performance at high temperatures. The Ge p-layer beneath the Silicon Fin increases electron current density and enhances device performance. Two high thermal conductivity 4H-SiC boxes are placed below the source and drain regions to overcome SHE. The pL-JL-FinFET exhibits the maximum transconductance of 148 μS, unity gain cut-off frequency of 455 GHz, and maximum available gain of 28.6 dB, which are improved by 208 %, 26 %, and 35 %, respectively, compared to regular JL-FinFET. Temperature analysis demonstrates suppressed SHE and better thermal stability than the regular JL-FinFET. Also, the pL-JL-FinFET shows superior thermal behavior in different fin shapes. The pL-JL-FinFET with a rectangular fin shape shows excellent linearity and high-frequency performance, achieving unconditional stability and minimum noise figure (NFmin) of less than 1 dB. An extracted small signal model is used to design a K-band low noise amplifier (LNA) with maximum NF and gain values of 0.75 dB and 18.7 dB. The pL-JL-FinFET opens opportunities for reliable, high-performance RF circuits while effectively managing thermal behavior.

Dielectric, reflection loss and physicochemical studies of Cr doped Ba–Sr based W type hexagonal ferrites for microwave absorption applications

The utilization of hexagonal structures in nano ferrites has been employed for absorption because of their dielectric, attenuation characteristics, and reflection losses. Electromagnetic pollution is one of the significant issues in cleaning the environment. Electronic devices produce pollution and are hazardous to human health. Therefore, ferrite materials have been used for absorption purposes. In this study, the impact of chromium substitution on the structural and dielectric specifications of the Barium-strontium-based W-type hexagonal ferrites has been investigated and used for microwave absorption application. The sol-gel auto-ignition process prepared w-type hexagonal ferrites with Ba0.5Sr0.5Mg2CrxFe16-xO27 (x = 0.0, 0.1, 0.2, 0.3, and 0.4). According to XRD examination, the formation of single-phase W-type hexagonal ferrites was proven. The synthesized composition is confirmed to be nanocrystalline because the calculated crystallite size value is in the nanometer range. FTIR analysis confirmed the structure of W-type hexagonal ferrite. Raman spectroscopic study examined the vibrational and rotational modes of molecules. Survey spectra of XPS, which include Ba, Sr, Mg, Fe, Cr, and O, confirmed the presence of all constituent elements. SEM analysis confirmed that the sample contains grains with a hexagonal platelet shape. The results showed that increasing chromium concentration reduced the dielectric permittivity, tan loss, and ac conductivity. At x = 0.4, the reflection loss value is very low. The recorded value is −79.62 dB, corresponding to a frequency of 5.92 GHz, with a thickness of 1.75 mm. Because of this, W-type hexagonal ferrites are suitable for a wide range of electronic applications, including microwave absorbers, high-density recording media, and multilayer chip inductors. These applications have made it possible to functionalize these materials in order to enhance device performance and lower the size, weight, and cost of devices while also fostering the development of new technologies that have significantly improved the quality of our daily lives.