ACS Applied Electronic Materials最新文献

To address the demand for temperature measurement in complex curved surfaces, this study designed and fabricated a high-temperature flexible temperature sensor. The sensor utilizes flexible mica as its substrate. A NiCr/NiSi thermocouple is deposited onto the mica substrate via magnetron sputtering. A protective SiO₂ layer and a Ti buffer layer are then applied over the thermocouple to form a multilayer composite structure, significantly enhancing the sensor’s oxidation resistance and stability in high-temperature environments. Performance testing indicates that after 1500 bending cycles, the maximum thermoelectric potential decay rate is 13.4%. Within the temperature range of room temperature to 560 °C, it exhibits a Seebeck coefficient of 17.66 μV/°C, a maximum repeatability error of ±2.17%, a temperature drift of 6.89 °C/h, and a dynamic response time as low as 20 μs. This sensor holds application potential in fields such as thermal management for high-power equipment, thermal runaway monitoring for electric vehicle battery cells, and thermal detection for smart wearable devices.

Gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs) are key to high-power and high-frequency electronics owing to their wide bandgap, high breakdown field, and ability to form a high-density two-dimensional electron gas (2DEG) at the AlGaN/GaN interface. For power-switching systems, enhancement-mode (E-mode) operation, where devices remain normally off at zero gate bias, is preferred for intrinsic failsafe behavior and reduced standby power. However, conventional E-mode strategies, such as deep gate recessing or p-type gate insertion, often introduce fabrication complexity, surface damage, and long-term instability. Here, we demonstrate a gate-localized CHF₃ plasma process that simultaneously produces a self-limiting recess with a fluorine-terminated surface, enabling a normally off AlGaN/GaN HEMT. Fluorine incorporation compensates polarization-induced charges and drives a positive shift in threshold voltage (V_th), whereas hydrogen species generated during plasma exposure passivate etch-induced Ga-related defects and suppress interface-trap formation. By confining plasma exposure to the gate region, this method mitigates surface degradation and charge trapping typically observed with CF₄ processing, achieving precise and stable V_th control without deep gate recessing. The fabricated devices exhibit normally off operation while maintaining low gate leakage under bias stress. This single step, lithographically confined approach offers a practical route toward E-mode GaN HEMTs for energy-efficient, high-frequency, and high-power electronic systems.

Inorganic piezoelectric films typically require high crystallization temperatures, making integration with flexible polymer substrates challenging. In this work, we develop a film transfer technique using a zinc oxide (ZnO) sacrificial layer to address this issue. By selectively etching the ZnO interlayer, we transfer large-area Nb_0.02-Pb(Zr_0.6Ti_0.4)O₃ (PZT) films onto flexible substrates, enabling the fabrication of a high-performance flexible piezoelectric energy harvester (FPEH). The resulting 2-μm-thick PZT film exhibits a high piezoelectric coefficient (d₃₃ ≈ 251 pm/V) and excellent dielectric properties. The FPEH produces output powers of 0.13 μW during periodic bending and 0.31 μW under applied pressure. Additionally, the device functions as a sensitive strain sensor capable of detecting human vocal signals during speech. This transfer approach facilitates the integration of high-efficiency piezoelectric materials into flexible electronics and self-powered systems.

Different from the (010) or (001) β-Ga₂O₃ thin-film growths, we report the growth of high-quality (011) β-Ga₂O₃ epitaxial films by metal–organic chemical vapor deposition (MOCVD) with thicknesses up to 20 μm. A series of β-Ga₂O₃ films were grown at growth rates of 2.86 and 5.5 μm/h on (011) β-Ga₂O₃ substrates using trimethylgallium (TMGa) and high-purity oxygen as precursors. Atomic force microscopy revealed extremely low root-mean-square (RMS) roughness across all samples, with values of 0.48–1.05 nm for film thicknesses up to 20 μm, representing the lowest reported roughness for as-grown β-Ga₂O₃ films of comparable thickness and scan area (5 × 5 μm²). X-ray diffraction confirmed excellent crystalline quality, with on-axis rocking curve full width at half-maximum (FWHM) values as low as 13.6 arcsec and off-axis values as low as 29.2 arcsec, revealing very low screw- and edge-type threading dislocation densities. Dent-type defect density, which increased with growth thickness, was significantly reduced at lower growth rates and further suppressed through the introduction of a buffer layer. Scanning transmission electron microscopy (STEM) imaging revealed a high crystalline quality of the as-grown films. Quantitative secondary ion mass spectrometry (SIMS) measured low background carbon and hydrogen levels along with minimal background silicon at or below the detection limit, even at growth rates up to ∼7.5 μm/h. The results from this work provide valuable guidance for the development of high-quality, thick β-Ga₂O₃ films via MOCVD, which are essential for realizing high-performance vertical power devices.

We investigated the degradation and recovery dynamics of Hf_xZr_1–xO₂ (HZO)-based ferroelectric field-effect transistors (FeFETs) under hydrogen contamination and thermal budgets, conditions relevant to advanced complementary metal-oxide-semiconductor (CMOS) processing, including back-end-of-line (BEOL) steps. High-pressure annealing (HPA) in a hydrogen-rich environment induced charge trapping and ferroelectric dipole pinning, leading to clockwise hysteresis and phase instability, as confirmed by electrical measurements and phase analysis. Subsequently, repeated program/erase cycling facilitated depinning, restoring polarization switching and partially recovering memory characteristics. These findings highlight the susceptibility of HZO to hydrogen-induced degradation in advanced integrations, such as monolithic 3D (M3D) with added hydrogen and thermal exposure. This underscores the need for hydrogen control and electric stress engineering to ensure reliable CMOS integration of FeFETs.

To overcome the limitations of flexible sensors relying on external power supply and single-mode detection, this study proposes a self-powered flexible sensor based on PVDF-TrFE-co-PEG Diamine@ionic liquid nanofiber membrane. This sensor integrates capacitive and piezoelectric dual modes within a compact sandwich structure, enabling high-sensitivity static pressure detection and self-powered dynamic signal generation without requiring an external power source or mode switching. This sensor exhibits ultrahigh sensitivity (32.28 kPa^–1, pressure < 12.5 kPa) in capacitive mode and can generate an open-circuit voltage as high as 1.51 V in piezoelectric mode, achieving efficient mechanical energy-to-electrical energy conversion. This will demonstrate broad application prospects in the fields of passive wearable electronics and electronic skin, providing a methodology for designing multifunctional integrated sensing systems.

The development of low-resistance electrical contacts in two-dimensional (2D) transition-metal dichalcogenides remains a major challenge due to strong Fermi-level pinning and high metal–semiconductor interfacial resistance. Lateral phase-engineered heterostructures formed via in-plane covalent bonding between semiconducting and metallic phases provide a promising route to atomically coherent interfaces with strong electronic coupling. Here, we use first-principles calculations to investigate the interfacial stability, bonding characteristics, and electronic structures of the lateral 2H/1T′-MoTe₂ heterojunctions. Among twenty possible geometries, six thermodynamically stable configurations are identified, and their relative stability is mainly dictated by local coordination and bonding orientation. Bonding and charge analyses show that interfacial stability and electronic coupling arise from the synergy among charge transfer, bond strength, and electronic states. Notably, the Schottky barrier height varies significantly with interface geometry, with the Z_5′ interface exhibiting an ultralow p-type barrier of 0.08 eV, indicative of nearly Ohmic contact. Furthermore, uniaxial strain effectively tunes band edges and barrier heights, while preserving robust interfacial bonding. These findings provide atomistic insights into the structure–property relationships of phase-engineered MoTe₂ interfaces and offer theoretical guidance for designing low-resistance 2D junctions.

Tin disulfide (SnS₂) stands out for its high absorption coefficient and efficient light absorption in the ultraviolet (UV) spectrum. However, the intrinsic defect-induced Fermi energy level pinning in tin disulfide limits its further utilization in optoelectronic detection. To overcome these shortcomings, high-quality, large-size SnS₂ nanosheets and cadmium sulfide (CdS) nanobelts were prepared by chemical vapor deposition (CVD) and physical vapor deposition (PVD), respectively. A SnS₂ Nanosheet/CdS nanobelt composite photodetector was fabricated and investigated. It is found that the composite photodetector exhibits superior performance in detecting UV–visible wavelengths. Compared to the SnS₂-based photodetector, the composite device demonstrates a higher responsivity (9760.4 A/W), a remarkable on/off current ratio (I_on/I_off) of 1.36 × 10⁶, rapid rise/decay time of 115/454 μs, a large external quantum efficiency of 3.46 × 10⁶ % and a specific detectivity of 4.36 × 10¹³ Jones. These outstanding properties are attributed to the high-quality crystal structure of the SnS₂ nanosheets and CdS nanobelts, as well as the formation of a type II energy band structure, which effectively separates charge carriers. A reliable imaging capability is exhibited by the SnS₂/CdS composite photodetector under ultraviolet illumination. The SnS₂-based photodetector shows great potential for the development of future optoelectronic devices.

The development of ambipolar two-dimensional (2D) field-effect transistors (FETs) based on transition metal dichalcogenides is hindered by Fermi-level pinning and the intrinsic trade-offs in using a single-contact geometry for both carrier types. Herein, a monolithic mixed-dimensional contact scheme is presented in which a one-step metallization seamlessly integrates one-dimensional high-work-function (Pd) edge contacts and 2D low-work-function (Ti) surface contacts. This architecture allows the spatial separation of hole and electron injection pathways on a WS₂ ambipolar channel, enabling independent contact optimization without a complex doping process. The resulting WS₂ FETs exhibit highly symmetric ambipolar characteristics, with on/off ratios exceeding 10⁷, comparable field-effect carrier mobilities of 182.5 (holes) and 159.0 cm²·V^–1·s^–1 (electrons), and Schottky barrier heights below 20 meV for both carrier types. Structural and temperature-dependent electrical analyses confirm the high crystallinity of the channel layer, which has a highly symmetrical contact resistance for both hole and electron carriers. Furthermore, the architecture enables the fabrication of complementary logic circuits, as demonstrated via a low-power WS₂-based inverter with a robust voltage transfer behavior. This mixed-dimensional contact scheme addresses the fundamental bottleneck in 2D device engineering and offers a scalable complementary metal-oxide-semiconductor-compatible route for ambipolar logic and reconfigurable electronics.

Achieving high external quantum efficiency (EQE) in AlGaN-based ultraviolet-B (UVB) light-emitting diodes (LEDs) remains a persistent challenge due to strong polarization-induced electric fields and poor electron–hole wave function overlap in strained quantum wells. Here, we report a decisive enhancement in carrier dynamics and optical efficiency by precisely engineering the QW thickness in a 40% relaxed AlGaN-based UVB LED grown on sapphire. Structural analyses confirm that controlled strain relaxation in the AlGaN quantum well effectively suppresses polarization fields, while compositional grading and optimized quantum-well thickness significantly improve carrier confinement and overlap. Systematic optimization of QW width mitigates the quantum-confined Stark effect, reducing the internal electric field from −0.97 to −0.32 MV cm^–1, thereby strengthening the electron–hole wave function overlap via a 7 nm thick QW and enhancing radiative recombination. A moderately Mg-doped p-type multiquantum-barrier electron-blocking layer and a partially relaxed n-type AlGaN electron injection layer further improve carrier confinement and injection efficiency. These combined effects yield an internal quantum efficiency of 80% and a predicted high external quantum efficiency exceeding 12%, nearly doubling that of conventional devices. This study establishes QW thickness modulation and polarization field management as practical and scalable strategies to overcome intrinsic polarization effects, enabling high-efficiency, mercury-free UVB emitters for next-generation disinfection, water purification, and smart-agriculture applications.