Search Results (13)

Beta-phase gallium oxide (β-Ga₂O₃) is a cutting-edge ultrawide bandgap (UWBG) semiconductor, featuring a bandgap energy of around 4.8 eV and a highly critical electric field strength of about 8 MV/cm. These properties make it highly suitable for next-generation power electronics and deep ultraviolet optoelectronics. Key advantages of β-Ga₂O₃ include the availability of large-size single-crystal bulk native substrates produced from melt and the precise control of n-type doping during both bulk growth and thin-film epitaxy. A comprehensive understanding of the fundamental growth processes, control parameters, and underlying mechanisms is essential to enable scalable manufacturing of high-performance epitaxial structures. This review highlights recent advancements in the epitaxial growth of β-Ga₂O₃ through various techniques, including Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Mist Chemical Vapor Deposition (Mist CVD), Pulsed Laser Deposition (PLD), and Low-Pressure Chemical Vapor Deposition (LPCVD). This review concentrates on the progress of Ga₂O₃ growth in achieving high growth rates, low defect densities, excellent crystalline quality, and high carrier mobilities through different approaches. It aims to advance the development of device-grade epitaxial Ga₂O₃ thin films and serves as a crucial resource for researchers and engineers focused on UWBG semiconductors and the future of power electronics. Full article

A spike-timing-dependent plasticity (STDP) device with a Ga-Sn-O (GTO) conductance change layer deposited by a mist-CVD method has been developed. First, the memristive characteristic is analyzed. Next, based on it, spike waveforms are determined. Finally, the STDP characteristic is successfully confirmed. This is an original report on the realization of an STDP characteristic using a thin film deposited by the mist-CVD method, which is achieved by the GTO properties and a well-designed clear methodology to realize a STDP characteristic from a memristive characteristic. Full article

Bismuth-based compounds have been regarded as a kind of promising material due to their narrow bandgap, high carrier mobility, low toxicity, and strong oxidation ability, showing potential applications in the field of photoelectrochemical (PEC) activities. They can be applied in sustainable energy production, seawater desalination and treatment, optical detection and communication, and other fields. As a member of the broader family of bismuth-based materials, β-Bi₂O₃ exhibits significant advantages for applications in engineering, including high photoelectric response, stability in harsh environments, and excellent corrosion resistance. This paper presents the synthesis of β-Bi₂O₃ thin films utilizing the mist chemical vapor deposition (CVD) method at the optimal temperature of 400 °C. Based on the β-Bi₂O₃ thin film synthesized at optimal temperature, a PEC-type photodetector was constructed with the highest responsivity R of 2.84 mA/W and detectivity D of 6.01 × 10¹⁰ Jones, respectively. The photodetection performance was investigated from various points like illumination light wavelength, power density, and long-term stability. This study would broaden the horizontal and practical applications of β-Bi₂O₃. Full article

α-Ga₂O₃ films were grown on a c-plane sapphire substrate by HCl-supported mist chemical vapor deposition with multiple solution chambers, and the effect of HCl support on α-Ga₂O₃ film quality was investigated. The growth rate monotonically increased with increasing Ga supply rate. However, as the Ga supply rate was higher than 0.1 mmol/min, the growth rate further increased with increasing HCl supply rate. The surface roughness was improved by HCl support when the Ga supply rate was smaller than 0.07 mmol/min. The crystallinity of the α-Ga₂O₃ films exhibited an improvement with an increase in the film thickness, regardless of the solution preparation conditions, Ga supply rate, and HCl supply rate. These results indicate that there is a low correlation between the improvement of surface roughness and crystallinity in the α-Ga₂O₃ films grown under the conditions described in this paper. Full article

Double buffer layers composed of (Al_xGa_1−x)₂O₃/Ga₂O₃ structures were employed to grow a Sn-doped α-Ga₂O₃ epitaxial thin film on a sapphire substrate using mist chemical vapor deposition. The insertion of double buffer layers improved the crystal quality of the upper-grown Sn-doped α-Ga₂O₃ thin films by blocking dislocation generated by the substrates. Rapid thermal annealing was conducted for the double buffer layers at phase transition temperatures of 700–800 °C. The slight mixing of κ and β phases further improved the crystallinity of the grown Sn-Ga₂O₃ thin film through local lateral overgrowth. The electron mobility of the Sn-Ga₂O₃ thin films was also significantly improved due to the smoothened interface and the diffusion of Al. Therefore, rapid thermal annealing with the double buffer layer proved advantageous in achieving strong electrical properties for Ga₂O₃ semiconductor devices within a shorter processing time. Full article

This study demonstrated the epitaxial growth of single-phase (111) CoO and (111) Co₃O₄ thin films on a-plane sapphire substrates using an atmospheric pressure mist chemical vapor deposition (mist-CVD) process. The phase structure of the grown cobalt oxide films was manipulated by controlling the growth temperature and process ambient, confirmed through X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, the electrical properties of Co₃O₄ films were significantly improved after thermal annealing in oxygen ambient, exhibiting a stable p-type conductivity with an electrical resistivity of 8.35 Ohm cm and a carrier concentration of 4.19 × 10¹⁶ cm⁻³. While annealing CoO in oxygen atmosphere, the Co₃O₄ films were found to be most readily formed on the CoO surface due to the oxidation reaction. The orientation of the atomic arrangement of formed Co₃O₄ was epitaxially constrained by the underlying CoO epitaxial layer. The oxidation of CoO to Co₃O₄ was largely driven by outward diffusion of cobalt cations, resulting in the formation of pores in the interior of formed Co₃O₄ films. Full article

All-inorganic perovskites, with their low-cost, simple processes and superior heat stability, have become potential candidate materials for photodetectors (PDs). However, they have no representative responsivity in the deep-ultraviolet (UV) wavelength region. As a new-generation semiconductor, gallium oxide (Ga₂O₃), which has an ultrawide bandgap, is appropriate for solar-blind (200 nm–280 nm) deep-UV detection. In this work, ultrawide-bandgap Ga₂O₃ was introduced into an inorganic perovskite device with a structure of sapphire/β-Ga₂O₃/Indium Zinc Oxide (IZO)/CsPbBr₃. The performance of this perovskite PD was obviously enhanced in the deep UV region. A low-cost, vacuum-free Mist-CVD was used to realize the epitaxial growth of β-Ga₂O₃ film on sapphire. By introducing the Ga₂O₃ layer, the light current of this heterojunction PD was obviously enhanced from 10⁻⁸ to 10⁻⁷, which leds its detectivity (D*) to reach 1.04 × 10¹² Jones under a 254 nm light illumination with an intensity of 500 μW/cm² at a 5 V bias. Full article

In this paper, the method for growing α-Ga₂O₃ films on c-plane sapphire substrates using an inexpensive fine-channel mist-CVD face-to-face heating plate was investigated. Because high temperatures can result in reactor deformation, expensive AlN ceramics resistant to deformation are used as the reactor fabrication material in traditional fine-channel mist-CVD equipment, which limits its use for promotion and research purposes. In this work, we used a face-to-face heating method to replace the traditional single-sided heating method which will reduce the requirement for equipment sealability. Therefore, cheap quartz can be used to replace expensive AlN ceramics to make reactors, which can greatly reduce the cost of mist-CVD equipment. We also investigated the effects of substrate temperature and carrier gas on the crystalline quality and surface morphology of α-Ga₂O₃ films. By optimizing the fabrication conditions, we obtained triangular grains with edges that were clearly visible in atomic force microscopy images. Using absorption spectrum analysis, we also found that the optical bandgap of the film reached 5.24 eV. Finally, we recorded a value of 508 arcsec for the full width at half maximum of the α-Ga₂O₃ (0006) diffraction peak in the X-ray diffraction pattern. Full article

In this study, an efficient hierarchical Co–Pi cluster/Fe₂O₃ nanorod/fluorine-doped tin oxide (FTO) micropillar three-dimensional (3D) branched photoanode was designed for enhanced photoelectrochemical performance. A periodic array of FTO micropillars, which acts as a highly conductive “host” framework for uniform light scattering and provides an extremely enlarged active area, was fabricated by direct printing and mist-chemical vapor deposition (CVD). Fe₂O₃ nanorods that act as light absorber “guest” materials and Co–Pi clusters that give rise to random light scattering were synthesized via a hydrothermal reaction and photoassisted electrodeposition, respectively. The hierarchical 3D branched photoanode exhibited enhanced light absorption efficiency because of multiple light scattering, which was a combination of uniform light scattering from the periodic FTO micropillars and random light scattering from the Fe₂O₃ nanorods. Additionally, the large surface area of the 3D FTO micropillar, together with the surface area provided by the one-dimensional Fe₂O₃ nanorods, contributed to a remarkable increase in the specific area of the photoanode. Because of these enhancements and further improvements facilitated by decoration with a Co–Pi catalyst that enhanced water oxidation, the 3D branched Fe₂O₃ photoanode achieved a photocurrent density of 1.51 mA cm⁻² at 1.23 V_RHE, which was 5.2 times higher than that generated by the non-decorated flat Fe₂O₃ photoanode. Full article

In this article, we demonstrate the van der Waals (vdW) epitaxial growth of ZnO layers on mica substrates through a low-temperature hydrothermal process. The thermal pretreatment of mica substrates prior to the hydrothermal growth of ZnO is essential for growing ZnO crystals in epitaxy with the mica substrates. The addition of sodium citrate into the growth solution significantly promotes the growth of ZnO crystallites in a lateral direction to achieve fully coalesced, continuous ZnO epitaxial layers. As confirmed through transmission electron microscopy, the epitaxial paradigm of the ZnO layer on the mica substrate was regarded as an incommensurate van der Waals epitaxy. Furthermore, through the association of the Mist-CVD process, the high-density and uniform distribution of ZnO seeds preferentially occurred on mica substrates, leading to greatly improving the epitaxial qualities of the hydrothermally grown ZnO layers and obtaining flat surface morphologies. The electrical and optoelectrical properties of the vdW epitaxial ZnO layer grown on mica substrates were comparable with those grown on sapphire substrates through conventional solution-based epitaxy techniques. Full article

This study examined the microstructural gradation in Sn-doped, n-type Ga₂O₃ epitaxial layers grown on a two-inch sapphire substrate using horizontal hot-wall mist chemical vapor deposition (mist CVD). The results revealed that, compared to a single Ga₂O₃ layer grown using a conventional single-step growth, the double Ga₂O₃ layers grown using a two-step growth process exhibited excellent thickness uniformity, surface roughness, and crystal quality. In addition, the spatial gradient of carrier concentration in the upper layer of the double layers was significantly affected by the mist flow velocity at the surface, regardless of the dopant concentration distribution of the underlying layer. Furthermore, the electrical properties of the single Ga₂O₃ layer could be attributed to various scattering mechanisms, whereas the carrier mobility of the double Ga₂O₃ layers could be attributed to Coulomb scattering owing to the heavily doped condition. It strongly suggests the two-step-grown, lightly-Sn-doped Ga₂O₃ layer is feasible for high power electronic devices. Full article

Hyperreactivity to stress may be one explanation for the increased risk of cardiovascular disease (CVD) in individuals with essential hypertension. We investigated blood lipid reactivity to the Montreal Imaging Stress Task (MIST), a psychosocial stressor, in hypertensive and normotensive men and tested for prospective associations with biological risk factors. Fifty-six otherwise healthy and medication-free hypertensive and normotensive men underwent the MIST. We repeatedly measured cortisol and blood lipid profiles (total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG)) immediately before and up to 1 h after stress. Lipid levels were corrected for stress hemoconcentration. Thirty-five participants completed follow-up assessment 2.9 ± 0.12 (SEM) years later. CVD risk was assessed by prospective changes in TC/HDL-C ratio, IL-6, D-dimer, and HbA1c from baseline to follow-up. The MIST induced significant changes in all parameters except TC (p-values ≤ 0.043). Compared with normotensives, hypertensives had higher TC/HDL-C-ratio and TG (p-values ≤ 0.049) stress responses. Blood lipid stress reactivity predicted future cardiovascular risk (p = 0.036) with increases in HbA1c (ß = 0.34, p = 0.046), IL-6 (ß = 0.31, p = 0.075), and D-dimer (ß = 0.33, p = 0.050). Our results suggest that the greater blood lipid reactivity to psychosocial stress in hypertensives, the greater their future biological CVD risk. This points to lipid stress reactivity as a potential mechanism through which stress might increase CVD risk in essential hypertension. Full article

This report systematically investigates the influence of different carrier gases (O₂, N₂, and air) on the growth of gallium oxide (Ga₂O₃) thin films on c-plane sapphire substrates by using the mist-CVD method. Although XRD and Raman measurements show that the pure corundum-structured α-Ga₂O₃ with single (0006) plane orientation was successfully obtained for all three different carrier gases, the crystal quality could be greatly affected by the carrier gas. When O₂ is used as the carrier gas, the smallest full-width at half maximum (FWHM), the very sharp absorption cutoff edge, the perfect lattice structure, the highest growth rate, and the smooth surface can be obtained for the epitaxial α-Ga₂O₃ film as demonstrated by XRD, UV-VIS, TEM, AFM (Atomic Force Microscope), and SEM measurements. It is proposed that the oxygen content in carrier gas should be responsible for all of these results. XPS (X-ray photoelectron spectroscopy) analysis also confirms that more oxygen elements can be included in epitaxial film when O₂ is used as the carrier gas and thus help improve the crystal quality. The proper carrier gas is essential for the high quality α-Ga₂O₃ growth. Full article