ACS Applied Electronic Materials最新文献

Compared to SrTiO₃-based 3d two-dimensional electron gases (2DEGs), KTaO₃-based 5d 2DEGs have much more exceptional physical properties, such as a higher Curie temperature of spin-polarized 2DEG, higher T_c for the 2DEG at superconducting state, and larger spin–orbit coupling. Herein, the CaZrO₃ (CZO) films were deposited on KTaO₃ (001) substrates at the deposition temperature varied from 700 °C to room temperature, and the conductive CZO/KTO interface was obtained at all deposition temperatures. The conductivity of the CZO/KTO heterointerface exhibits critical dependence on the film thickness, where the critical thickness for conduction increases from 3.2 to 6 nm when decreasing the deposition temperature from 700 °C to room temperature. Moreover, the electric properties of the heterointerface grown at room temperature can be modulated strongly by the light illumination. The strength of the spin–orbit coupling exhibits large relative variation with the carrier density. Under the light illumination, the strength of the spin–orbit coupling increases from ∼3.9 × 10^–12 eV m to the maximum of ∼9 × 10^–12 eV m, with the maximal change of the carrier density of only 3 × 10¹² cm^–2. The present work demonstrates an effective tuning of the special 5d-electron-based 2DEGs by light illumination, showing a feasible way for advanced optoelectronic device application.

Micromechanical resonators with very low mass are highly desirable for sensing and transduction applications. Layered materials (LMs) can be used to fabricate single- to few-atom thick suspended membranes, representing the ultimate limit to low mass. Transition-metal dichalcogenides (TMDs), such as WSe₂, are particularly compelling because they can host spatially confined excitons in single layer (1L), potentially enabling the creation of nonclassical mechanical states and interconnects between quantum networks and processors. However, these exciting prospects have been tempered by low device yields, invasive methods for detecting resonator motion, and high mechanical damping. Here, we report the creation of mechanical resonators by suspending 1L-WSe₂ across a 90 × 90 array of 2.5-μm diameter holes with a > 75% success rate. We detect the resonator room-temperature (RT) Brownian motion and measure resonator mass to quantify contamination, using below-bandgap laser interferometry. We investigate the relation between frequency, diameter, and mechanical quality factor, which can exceed 1000 in our devices. We find the dependence agrees with the effect of dissipation dilution, highlighting the importance of reducing mechanical mode-bending. Key to this is the large-scale, high-quality arrays that make it possible to access a frequency range that surpasses previous works. Further, the ability to fabricate large numbers of 1L resonators, and the simplicity of probing their motion without electrodes or an underlying reflective substrate, facilitates previously hard-to-reach configurations, such as resonators in phononic crystals or within optical cavities.

Soft sensors that emulate the modulus of human skin have shown significant potential for wearable sensing applications by ensuring robust, conformal contact that enables the acquisition of high-quality signals. Organic thin-film transistor (TFT)-based pixelated soft sensor arrays have been crucial for advanced spatiotemporal signal measurements, thanks to their active-matrix configuration, which minimizes signal crosstalk. Despite these advancements, challenges such as limited sensitivity, high power consumption, and the need for cost-effective, large-area integration technologies persist, hindering their practical application. This paper explores strategies for developing high-performance TFT-based soft sensing arrays. We begin by discussing the design principles for organic TFT-based sensors, offering strategies to enhance sensitivity while reducing power consumption, with a focus on the underlying device physics. We also introduce a method for ultrathin, large-area, high-performance TFT integration using systematic inkjet printing technology. To demonstrate the practical applications of our approach, we present high-performance spatiotemporal measurements of arterial pulse waves using active-matrix pressure and optical sensing arrays. The low-power, high-sensitivity, and large-area integration strategies discussed in this paper are expected to significantly advance organic TFT-based sensors, paving the way for their practical application in healthcare, wearable technology, and environmental monitoring.

Layered Sn- and Ge-based monochalcogenides have been known as promising semiconductor materials with appropriately narrow band gaps close to those of Si and GaAs. On the other hand, Pb-based ones possess much narrower band gaps and adopt the cubic rock-salt (RS)-type structure under ambient conditions, and their layered structures are considered thermodynamically unstable. We recently succeeded in the stabilization of GeS-type layered structures in lightly Sn-doped PbS by the combination of a high-temperature solid-state reaction with thermal quenching. In this paper, we have comprehensively investigated the relationship between the crystal structures, electronic structures, and also electronic and thermal transport properties of (Pb_1–xSn_x)S (x = 0–1). It is experimentally confirmed that an equilibrium phase of layered GeS-type Sn-rich (Pb_1–xSn_x)S is a p-type semiconductor at x ≥ 0.7, whereas n-type conduction is observed at x = 0.5 and 0.6. In contrast, the stabilized nonequilibrium layered phase with 0.2 ≤ x ≤ 0.4 is an n-type semiconductor with the band gaps of 1.18–1.22 eV, and the electron density increases up to 6.4 × 10¹⁷ cm^–3 in (Pb_0.8Sn_0.2)S. Furthermore, the layered nonequilibrium phase exhibits an ultralow room-temperature thermal conductivity of 0.40–0.65 W/(mK), much lower than those of both end members, i.e., GeS-type SnS (x = 1) and RS-type PbS (x = 0). Based on first-principles electron and phonon transport calculations, layered n-type (Pb_0.75Sn_0.25)S potentially shows a high thermoelectric figure of-merit of 0.34 even at 300 K under an optimized electron concentration. The controllability of bipolar carrier polarity in layered (Pb_1–xSn_x)S alongside the low thermal conductivity is an advantageous characteristic for applications based on p–n homojunctions, such as photovoltaics and thermoelectrics.

While two-dimensional (2D) materials have shown great promise for scaling technology nodes beyond the limits of silicon devices, key challenges remain for realizing high-quality and practical 2D field-effect transistors (FETs), including lowering contact resistance, demonstrating device structures with high electrical stability, reducing interface charge trapping, and integrating n- and p-FETs for beyond-complementary metal oxide semiconductor devices. High contact resistance often stems from Schottky contacts and Fermi level pinning and can be reduced by local doping or transferred contacts, respectively. However, these approaches to date have been mutually incompatible. Here, we combine both into a single structure and demonstrate a locally doped, transfer-contact stack containing access regions adjacent to the metal via contacts embedded in hexagonal boron nitride. Doping is applied by oxygen plasma treatment of access regions, while the fully encapsulated WSe₂ channel remains pristine, creating a lateral p⁺–i–p⁺ junction. We demonstrate a reduction in contact resistance by up to >30,000 times with the contact strategy, with a lowest individual contact resistance of ∼3.6 kΩ · μm, limited by the doping density at the contacts. Our results highlight increasing doping in the contact region as being crucial for achieving improved contact resistance in p-type WSe₂ devices. For our FET devices, the geometry of gates, doped access regions, and the channel are all defined by an electron beam lithography giving full and precise control over size and position. The p-FET behavior is strongly enhanced with a high on/off ratio up to 10⁷, but ambipolar characteristics from the intrinsic channel are still retained. Negligible, temperature-independent hysteresis is achieved from T = 10 to 300 K, with only back gate carrier control. High electrical stability is evident in the excellent reproducibility of transfer characteristics between multiple contact sets on a single device and different devices. The doping reduces contact resistance by reducing the Schottky barrier height and width, achieving Ohmic IV characteristics. The doping appears very stable, with negligible degradation of performance, keeping the device for 50 days in atmosphere. This reasonably simple device structure incorporates two important strategies to enhance contact quality, improving p-FET performance and retaining intrinsic channel quality.

The flexible electrothermal heaters based on the Joule heating effect have attracted extensive attention in recent years due to their wide range of applications in personal thermal management and wearable devices. However, the fabrication of this kind of flexible heater with high performance but at low cost remains a challenge. Here in this work, a high-performance and flexible electrothermal heater was developed through layer-by-layer self-assembly of graphite nanoplates (GNPs) and carbon black (CB) on paper driven by capillarity. The resistivity of the assembled GNP/CB layer was around 0.02 Ω·cm after dip-coating 10 times. The heater reached a maximum temperature of 197.3 °C with a heating rate of 23 °C s^–1 under a relatively low voltage of 6 V. Importantly, no attenuation of the heating performance was observed under deformation of the device. This flexible electrothermal heater may find versatile applications, including water heating, deicing, wearable devices, and medical treatments.

Flexible conducting ceramics offer exciting potential for advanced high-temperature electronic and thermal management applications, but challenges remain in achieving both flexibility and high electrical conductivity without compromising the material’s structural integrity. In this study, we present a flexible metallized E-glass fiber network formed via mixing copper molecular ink with ceramic fibers (copper-coated aluminum borosilicate) to enable strain sensing under harsh conditions, exhibiting a gauge factor of 1.34 and a response time of 100 ms at room temperature. A silicon carbide preceramic precursor was further coated to achieve a synergistic combination of high-temperature oxidation resistance. The flexible sensor functions effectively at temperatures of up to 400 °C, making it suitable for high-temperature environments, with a gauge factor of 0.181. Additionally, incorporating a printed dipole antenna allows for a self-powered system that can wirelessly respond to real-time applied strains.

The consumption of indium (In) is an obstacle for terawatt-scale silicon heterojunction (SHJ) solar cells. To reduce the use of In and achieve sustainable development, the development of economical and environmentally friendly transparent electrodes has become a critical issue. Here, we report crystalline silicon heterojunction solar cells with reactive plasma deposition (RPD) grown ZnO:Ga₂O₃ (GZO) at room temperature as a transparent conductive oxide (TCO) layer. Meanwhile, SHJ solar cells with magnetron sputtered indium tin oxide (ITO) transparent conductive layers are compared as reference. GZO thin films exhibit good crystallinity with (002) preferred orientation. The optical and electrical properties of GZO thin films with different doping concentrations have been systematically studied. Under the condition of 3.0 wt % doping concentration and 545 nm thickness, the carrier concentration and electron mobility of GZO film reach 2.95 × 10²⁰/cm³ and 32.56 cm²/V·s, respectively; thus, a resistivity of 7.46 × 10^–4 Ω cm is obtained. The average transmittance of the glass/GZO film is 83.3% in the wavelength range of 400–1200 nm. The contact resistance for GZO/n-a-Si:H is calculated to be 48.0 mΩ cm². GZO-SHJ solar cell exhibits a higher minority carrier lifetime and thus higher Voc due to less interface damage during thin film deposition. The GZO-TCO film is used in a SHJ solar cell, achieving a device efficiency of 21.48%. The results shows that gallium doping of GZO increases electrical conductivity and regulates oxygen vacancies. In-free TCO grown by a low-bombardment RPD technique will contribute to boosting the development of the SHJ solar cell photovoltaic industry.

The high theoretical capacity and low electrochemical potential make lithium metal the most promising material to replace the graphite anode. However, lithium dendrite growth is the key problem that limits the development of lithium metal batteries. As a solid electrolyte, the gel polymer electrolyte (GPE) possesses a certain ability to inhibit the growth of lithium dendrites compared with a liquid electrolyte, but the inhibition mechanism is not very clear. In this work, through the regulation of GPE cross-linking density, we verify that the cross-linked GPE network has a certain influence on the solvation structure of lithium ions. The increased cross-linking density of GPE induces the Li⁺ solvated sheath dominated by contact ion pairs/solvent-separated ion pairs and Li⁺ aggregates, which is conducive to the formation of stable LiF-rich SEIs to resist lithium dendrites. The high cross-linked GPE-based LiFePO₄ full battery also exhibits a high capacity retention rate of 81.9% even after 220 cycles at a rate of 0.2C and 90.1% after 140 cycles at a rate of 0.5C. The inhibiting mechanism of lithium dendrites by the cross-linked GPE is described for the first time, which provides a better idea for the design of GPE.

Defects in the sidewall interfaces are critical to light-emitting efficiency of micro-light emitting diodes (μLEDs) for display applications. The efficiency decreases sharply when the LED chip size is smaller than 10 × 10 μm² because the sidewall defect-induced nonradiative recombination process prevails. In this work, we demonstrate the efficiency improvement of GaN-based μLEDs with sizes as small as 4 × 4 μm². Using N₂ plasmon treatment at 250 °C to repair sidewall damage, the light output power of an LED with a mesa size of 4 × 4 μm² is improved by 97.29% compared to the reference device without treatment at an injection current density of 25 A/cm². Additionally, compared to a reference device with a mesa area of 100 × 100 μm², the optical output power density of the 4 × 4 μm² device shows only a 27.11% drop. To understand the effect of nitrogen plasmon treatment on the interfaces, we conducted EDX (energy-dispersive X-ray spectroscopy) and TRPL (time-resolved photoluminescence) analysis on the sidewalls of p-type GaN and the quantum well active region. We concluded that incorporating nitrogen atoms to repair the dangling bonds and, thus, a more balanced Ga/N ratio helps reduce defects and thus improve sidewall radiative efficiency.