Search Results (83)

In this paper, a novel enhancement-mode β-Ga₂O₃-based FinFET structure with a gate formed by the NiO/β-Ga₂O₃ heterojunction named HJ-FinFET has been proposed, and the excellent performance of the device has also been demonstrated. The primary operational mechanism of this structure involves integrating p-type NiO on both sides of the fin-shaped channel, which forms p-n junctions with β-Ga₂O₃. The depletion regions thus generated are utilized to establish electron channels, enabling enhancement-mode operation. The reverse p-NiO/n-Ga₂O₃ heterojunction diode is integrated to reduce the reverse free-wheeling loss. Compared with the conventional devices, the threshold voltage of the HJ-FinFET is greatly improved, and normally off operation is realized, showing a positive threshold voltage of 2.14 V. Meanwhile, the simulated breakdown voltage of the HJ-FinFET reaches 2.65 kV with specific on-resistance (R_on,sp) of 2.48 mΩ·cm² and the power figure of merit (PFOM = BV²/R_on,sp) reaches 2840 MW/cm², respectively. In addition, the influence of the doping concentration of the heterojunction layer constituting the gate, the doping concentration of the drift layer, and the channel width on the electrical characteristics of the devices were focused on. This structure provides a feasible idea for high-performance β-Ga₂O₃-based FinFET. Full article

H₂S detection is critical for personal and industrial safety. Generally, metal oxide-based H₂S sensors exhibit no response at room temperature (RT). In this study, CuO/ZnWO₄ (C-ZWO) nanocomposites were prepared via a two-step hydrothermal process and applied to RT H₂S sensing. The results show that the C-ZWO sensors exhibit an elevated response value at RT and balanced gas-sensing properties at 100 °C. Significantly, the response value of a 10% C-ZWO sensor to 25 ppm of H₂S at RT is 651.6 with a response time of 78 s, which is 310.3 times that of the ZnWO₄ sensor (2.1). The systemic characterization results suggest that the enhanced RT H₂S-sensing properties are ascribed to the synergistic effects of the growth-specific surface area and oxygen vacancy occupancy, the enhanced oxygen reduction ability, and the formation of the p–n heterojunction structure between CuO and ZnWO₄. The C-ZWO nanocomposites possess added active sites for H₂S adsorption and dissociation, with the p–n heterojunction giving rise to higher electrical resistance, and thus, the follow-up produces a high response value even at RT. Full article

This study systematically investigates the effects of trap concentration on self-heating and terahertz (THz) responses in GaN HEMTs using Sentaurus TCAD. Traps, inherently unavoidable in semiconductors, can be strategically introduced to engineer specific energy levels that establish competitive dynamics between the electron momentum relaxation time and the carrier lifetime. A simulation-based exploration of this mechanism provides significant scientific value for enhancing device performance through self-heating mitigation and THz response optimization. An AlGaN/GaN heterojunction HEMT model was established, with trap concentrations ranging from 0 to $5\times {10}^{17} {\mathrm{c}\mathrm{m}}^{-3}$. The analysis reveals that traps significantly enhance channel current (achieving 3× gain at $1\times 10^{17} {\mathrm{c}\mathrm{m}}^{-3}$) via new energy levels that prolong carrier lifetime. However, elevated trap concentrations (>$1\times {10}^{16} {\mathrm{c}\mathrm{m}}^{-3}$) exacerbate self-heating-induced current collapse, reducing the min-to-max current ratio to 0.9158. In THz response characterization, devices exhibit a distinct DC component (${\mathrm{U}}_{\mathrm{d}\mathrm{c}}$) under non-resonant detection ($\mathsf{\omega }\mathsf{\tau }\ll 1$). At a trap concentration of $1\times {10}^{15} {\mathrm{c}\mathrm{m}}^{-3}$, ${\mathrm{U}}_{\mathrm{d}\mathrm{c}}$ peaks at $0.12 \mathrm{V}$ when ${\mathrm{V}}_{\mathrm{g}}\mathrm{D}\mathrm{C}=-7.8 \mathrm{V}$. Compared to trap-free devices, a maximum response attenuation of 64.89% occurs at ${\mathrm{V}}_{\mathrm{g}}\mathrm{D}\mathrm{C}=-4.9 \mathrm{V}$. Furthermore, ${\mathrm{U}}_{\mathrm{d}\mathrm{c}}$ demonstrates non-monotonic behavior with concentration, showing local maxima at $4\times {10}^{15} {\mathrm{c}\mathrm{m}}^{-3}$ and $7\times {10}^{15} {\mathrm{c}\mathrm{m}}^{-3}$, attributed to plasma wave damping and temperature-gradient-induced electric field variations. This research establishes trap engineering guidelines for GaN HEMTs: a concentration of $4\times {10}^{15} {\mathrm{c}\mathrm{m}}^{-3}$ optimally enhances conductivity while minimizing adverse impacts on both self-heating and the THz response, making it particularly suitable for high-sensitivity terahertz detectors. Full article

Recent advancements in biomarker technology have revolutionized diagnostic and monitoring applications, yet their potential in food quality assessment remains largely untapped. Herein, we report a breakthrough in gas-sensitive nanocomposite engineering through the design of α-Fe₂O₃-NiO heterostructures synthesized via a single-step hydrothermal protocol. The introduction of NiO led to increased oxygen vacancies and active sites, thereby reducing the sensor’s operating temperature. Additionally, the P-N heterojunction structure promoted the redistribution of electrons and hole, thus enhancing its conductivity. The optimized sensor exhibited high sensitivity (75.5% at 100 ppm), fast response/recovery (20 s/92 s), and perfect selectivity for NH₃ at room temperature. In the end, based on this sensor and combined with a Programmable Logic Controller (PLC), a rapid and nondestructive meat spoilage detection system was constructed to reflect the degree of spoilage of meat with the help of NH₃ concentration, providing a valuable strategy for the application of biomarker detection in the food industry. Full article

Triethylamine (TEA), a volatile organic compound (VOC), has important applications in industrial production. However, TEA has an irritating odor and potential toxicity, making it necessary to develop sensitive TEA gas sensors with high efficiency. This study focused on preparing LaFeO₃ nanoparticles modified by SnS₂ nanosheets (SnS₂/LaFeO₃ composite) using a hydrothermal method together with sol–gel technique. According to the comparison results of the gas-sensing performance between pure LaFeO₃ and SnS₂/LaFeO₃ composite with varying composition ratios, 5% SnS₂/LaFeO₃ sensor had a sensitivity for TEA that was 3.2 times higher than pure LaFeO₃ sensor. The optimized sensor operates at 140 °C and demonstrates strong stability, selectivity, and long-term durability. Detailed analyses revealed that the SnS₂ nanosheets enhanced oxygen vacancy (O_V) content and carrier mobility through heterojunction formation with LaFeO₃. This study provides insights into improving gas-sensing performance via p-n heterostructure design and proposes a novel LaFeO₃-based material for TEA detection. Full article

Thin TiO₂–SnO₂ nanocomposite films with high gas sensitivity to NO₂ were synthesized by oxidative pyrolysis and comprehensively studied. The composite structure and quantitative composition of the obtained film nanomaterials have been confirmed by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy, which causes the presence of n-n heterojunctions and provides improved gas-sensitive properties. The sensor based on the 3TiO₂–97SnO₂ film has the maximum responses, which is explained by the existence of a strong surface electric field formed by large surface potentials in the region of TiO₂–SnO₂ heterojunctions detected by the Kelvin probe force microscopy method. Exposure to low-intensity radiation (no higher than 0.2 mW/cm², radiation wavelength—400 nm) leads to a 30% increase in the sensor response relative to 7.7 ppm NO₂ at an operating temperature of 200 °C and a humidity of 60% RH. At room temperature (20 °C), under humidity conditions, the response is 1.8 when exposed to 0.2 ppm NO₂ and 85 when exposed to 7.7 ppm. The lower sensitivity limit is 0.2 ppm NO₂. The temporal stability of the proposed sensors has been experimentally confirmed. Full article

We propose a novel ultraviolet (UV) phototransistor (PT) architecture based on an AlGaN/GaN high electron mobility transistor (HEMT) with a buried p-GaN layer. In the dark, the polarization-induced two-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction interface is depleted by the buried p-GaN and the conduction channel is closed. Under UV illumination, the depletion region shrinks to just beneath the AlGaN/GaN interface and the 2DEG recovers. The retraction distance of the depletion region during device turn-on operation is comparable to the thickness of the AlGaN barrier layer, which is an order of magnitude smaller than that in the conventional p-GaN/AlGaN/GaN PT, whose retraction distance spans the entire GaN channel layer. Consequently, the proposed device demonstrates significantly enhanced weak-light detection capability and improved switching speed. Silvaco Atlas simulations reveal that under a weak UV intensity of 100 nW/cm², the proposed device achieves a photocurrent density of 1.68 × 10⁻³ mA/mm, responsivity of 8.41 × 10⁵ A/W, photo-to-dark-current ratio of 2.0 × 10⁸, UV-to-visible rejection ratio exceeding 10⁸, detectivity above 1 × 10¹⁹ cm·Hz^1/2/W, and response time of 0.41/0.41 ns. The electron concentration distributions, conduction band variations, and 2DEG recovery behaviors in both the conventional and novel structures under dark and weak UV illumination are investigated in depth via simulations. Full article

Self-powered ultraviolet photodetectors hold significant potential for diverse applications across both military and civilian fields. Owing to its wide bandgap, high electron mobility, and adaptability to various substrates, gallium oxide (Ga₂O₃) serves as a crucial material for fabricating self-powered ultraviolet photodetectors. Photodetectors based on p-n heterojunctions of conductive polymers and gallium oxide have great application potential benefiting from unique advantages of conductive polymers. This review provides an extensive overview of typical ultraviolet photodetectors based on conductive polymer/gallium oxide heterojunctions, focusing on the physical structure, fabrication process, and photoelectric properties of heterojunction devices formed by Ga₂O₃ with conductive polymers like polythiophene, polyaniline, and polycarbazole, etc. Different conductive polymers yield varying performance improvements in the fabricated devices: polythiophene/Ga₂O₃ devices exhibit high conductivity and flexible bandgap tuning to meet diverse wavelength detection needs; PANI/Ga₂O₃ devices feature simple fabrication and low cost, with doping control to enhance charge carrier transport efficiency; polycarbazole/Ga₂O₃ devices offer high thermal stability and efficient hole transport. Among them, the polythiophene/Ga₂O₃ device demonstrates the most superior overall performance, making it the ideal choice for high-performance Ga₂O₃-based photodetectors and a representative of such research. This review identifies the existing technical challenges and provides valuable insights for designing more efficient Ga₂O₃/conductive polymer heterojunction photodetectors. Full article

Ammonia (NH₃) is a common agricultural gas, and its accurate detection is critical to agricultural production. In this study, nano-CuO/CeO₂ composites were prepared to achieve a wide range of ammonia detection at room temperature. Characterization data verified the composite heterojunction structure of CuO/CeO₂, which demonstrates an outstanding large specific surface area for ammonia detection. It provides more active sites for NH₃ molecules, which brings a very high response to ammonia (70.3% @100 ppm NH₃), a large detection range (0.5–200 ppm NH₃), and a fast response/recovery time (13 s/17 s @20 ppm NH₃). Systematic testing showed that the nano-CuO/CeO₂ composites also exhibit excellent extended-term stability and selectivity. Further studies showed that the p-n heterojunction structure of CuO/CeO₂ allowed the composite to retain its gas-sensitive properties to ammonia, in addition to the improved ammonia-detection range of the composite based on the synergistic effect of these two materials. The mechanism of CuO/CeO₂ heterojunction nanocomposites towards ammonia detection was also elucidated from a microscopic perspective at the molecular level. Finally, a triboelectric nanogenerator (TENG) that can be driven by wind power has been prepared, upon which the feasibility of the combination of the TENG and the ammonia sensor to realize environmental monitoring was investigated. Full article

The SnO₂@Bi₂O₃ core-shell heterojunction structure was designed and synthesized via a hydrothermal method, and the structure and morphology of the synthesized samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Based on the conclusions from XRD and SEM, it can be observed that as the hydrothermal temperature increases, the content of Bi₂O₃ coated on the surface of SnO₂ spheres gradually increases, and the diameter of Bi₂O₃ nanoparticles also increases. At a hydrothermal temperature of 160 °C, the SnO₂ spheres are fully coated with Bi₂O₃ nanoparticles. This paper investigated the gas-sensitive performance of the SnO₂@Bi₂O₃ sensor towards ethanol gas. Gas sensitivity tests at the optimal operating temperature of 300 °C showed that the composite prepared at 160 °C achieved a response value of 19.7 for 100 ppm ethanol. Additionally, the composite exhibited excellent response to 100 ppm ethanol, with a response time of only 4 s, as well as good repeatability. The excellent gas-sensitive performance of the SnO₂@Bi₂O₃ core-shell heterojunction towards ethanol gas is attributed to its p-n heterojunction material properties. Its successful preparation contributes to the realization of high-performance heterostructure ethanol gas sensors. Full article

This work presents a simple process for the development of flexible acetone gas sensors based on zinc oxide/graphene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate). The gas sensors were prepared by inkjet printing, which was followed by a metal sparking process involving different sparking times. The successful decoration of ZnO nanoparticles (average size ~19.0 nm) on the surface of the graphene–PEDOT:PSS hybrid ink was determined by characterizations, including Raman spectroscopy, Fourier transform infrared spectroscopy, field-emission transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffractometry. The ZnO nanoparticle-decorated graphene–PEDOT:PSS with a sparking time of 2 min exhibited the highest response of 71.9% at 10 ppm of acetone, above those of samples treated with other sparking times and the undecorated control. In addition, the optimal sensor revealed high selectivity for acetone over several other kinds of gases, such as ammonia, toluene, dimethylformamide, ethanol, methanol, and benzene, at room temperature. The gas sensor also revealed a low limit of detection (0.4 ppm), high sensitivity (6.18 ppm⁻¹), and high stability (5-week long-term) to acetone. The response and recovery times of the sensor were found to be 4.6 min and 4.2 min, respectively. The acetone-sensing mechanism was attributed to the formation of p-n heterojunctions, which were responsible for the significantly enhanced sensitivity. Full article

As a VOC, ethanol can be found in human exhaled breath, and its concentration can be used as a biomarker of human liver disease. To detect trace-level concentrations of ethanol, an ultrasensitive ethanol sensor was developed based on a dual-nanoparticle In₂O₃/SnO₂ composite that was prepared by hydrothermal synthesis, and its suspension was dipped on a flat electrode to form a gas sensor. The nanocomposite was characterized by an SEM (scanning electron microscope), XRD (X-ray diffraction), and a TEM (transmission electron microscope), and the nanoparticle structure was observed. The experimental results showed that gas sensors based on the In₂O₃/SnO₂ nanocomposite had higher responses compared to sensors based on pure In₂O₃. Among the nanocomposites, the one with a In₂O₃-to-SnO₂ mol ratio of 1:8 was used in the sensor with the highest response of 1.41 to 100 ppb ethanol at 150 °C, which also exhibited good repeatability. The ultrasensitive response to ethanol can be attributed to the faster electron migration rate and the increase in oxygen-absorbing sites caused by the n-n heterojunction in the nanocomposite. Due to its low detection limit, good repeatability, and relatively high responses in high humidity, this sensor has a potential application in exhaled breath detection. Full article

Semiconducting metal oxides with nanofiber (NF) morphologies are among the most promising materials for the realization of gas sensors. In this study, we have prepared electrospun ZnO-NiO composite NFs with different amounts of NiO (0, 20, 40, 60 and 80% wt%) for the systematic study of ethanol gas sensing. The fabricated composite NFs were annealed at 600 °C for crystallization. Based on characterization studies, NFs were produced with desired morphologies, phases, and chemical compositions. Ethanol gas sensing studies revealed that the sensor with 40 wt% NiO had the highest response (3.6 to 10 ppm ethanol) at 300 °C among all gas sensors. The enhanced gas response was ascribed to the formation of sufficient amounts of p-n NiO-ZnO heterojunctions, NFs’ high surface areas due to their one-dimensional morphologies, and acid–base interactions between ZnO and ethanol. This research highlights the need for the optimization of ZnO-NiO composite NFs so that they achieve the highest sensing response, which can be extended to other similar metal oxides. Full article

The development of energy-efficient, sensitive, and reliable gas sensors for monitoring NO₂ concentrations has garnered considerable attention in recent years. In this manuscript, TiO₂ nanotube arrays/reduced graphene oxide nanocomposites with varying rGO contents (TiO₂ NTs/rGO) were synthesized via a two-step method for room temperature NO₂ gas detection. From SEM and TEM images, it is evident that the rGO sheets not only partially surround the TiO₂ nanotubes but also establish interconnection bridges between adjacent nanotubes, which is anticipated to enhance electron–hole separation by facilitating electron transfer. The optimized TiO₂ NTs/rGO sensor demonstrated a sensitive response of 19.1 to 1 ppm of NO₂, a 5.26-fold improvement over the undoped TiO₂ sensor. Additionally, rGO doping significantly enhanced the sensor’s response/recovery times, reducing them from 24 s/42 s to 18 s/33 s with just 1 wt.% rGO. These enhancements are attributed to the increased specific surface area, higher concentration of chemisorbed oxygen species, and the formation of p-n heterojunctions between TiO₂ and rGO within the nanocomposites. This study provides valuable insights for the development of TiO₂/graphene-based gas sensors for detecting oxidizing gases at room temperature. Full article

This study investigates the stability, electronic structure, and optical properties of the GaN/g-C₃N₄ heterojunction using the plane wave super-soft pseudopotential method based on first principles. Additionally, an external electric field is employed to modulate the band structure and optical properties of GaN/g-C₃N₄. The computational results demonstrate that this heterojunction possesses a direct band gap and is classified as type II heterojunction, where the intrinsic electric field formed at the interface effectively suppresses carrier recombination. When the external electric field intensity (E) falls below −0.1 V/Å and includes −0.1 V/Å, or exceeds 0.2 V/Å, the heterojunction undergoes a transition from a type II structure to the superior Z-scheme, leading to a significant enhancement in the rate of separation of photogenerated carriers and an augmentation in its redox capability. Furthermore, the introduction of a positive electric field induces a redshift in the absorption spectrum, effectively broadening the light absorption range of the heterojunction. The aforementioned findings demonstrate that the optical properties of GaN/g-C₃N₄ can be precisely tuned by applying an external electric field, thereby facilitating its highly efficient utilization in the field of photocatalysis. Full article