| 1. |
- Serban, Alexandra, et al.
(författare)
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Selective-area growth of single-crystal wurtzite GaN nanorods on SiOx/Si(001) substrates by reactive magnetron sputter epitaxy exhibiting single-mode lasing
- 2017
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Selective-area growth (SAG) of single-crystal wurtzite GaN nanorods (NRs) directly onto Si(001) substrates with un-etched native SiOx amorphous layer, assisted by a patterning TiNx mask fabricated by nanosphere lithography (NSL), has been realized by reactive magnetron sputter epitaxy (MSE). The GaN NRs were grown vertically to the substrate surface with the growth direction along c-axis in the well-defined nano-opening areas. A 5-step structural and morphological evolution of the SAG NRs observed at different sputtering times depicts a comprehensive growth model, listed in sequence as: formation of a polycrystalline wetting layer, predominating c-axis oriented nucleation, coarsening and coalescence of multi-islands, single NR evolution, and finally quasi-equilibrium crystal shape formation. Room-temperature cathodoluminescence spectroscopy shows a strong GaN bandedge emission with a uniform luminescence across the NRs, indicating that the SAG NRs are grown with high quality and purity. In addition, single-longitudinal-mode lasing, attributed to well-faceted NR geometry forming a Fabry-Perot cavity, was achieved by optical pumping, paving a way for fabricating high-performance laser optoelectronics using MSE.
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| 2. |
- Bairagi, Samiran, et al.
(författare)
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Formation of quaternary Zn(AlxGa1−x)2O4 epilayers driven by thermally induced interdiffusion between spinel ZnGa2O4 epilayer and Al2O3 substrate
- 2023
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Ingår i: Materials Today Advances. - : Elsevier. - 2590-0498. ; 20
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Tidskriftsartikel (refereegranskat)abstract
- Zinc aluminogallate, Zn(AlxGa1−x)2O4 (ZAGO), a single-phase spinel structure, offers considerable potential for high-performance electronic devices due to its expansive compositional miscibility range between aluminum (Al) and gallium (Ga). Direct growth of high-quality ZAGO epilayers however remains problematic due to the high volatility of zinc (Zn). This work highlights a novel synthesis process for high-quality epitaxial quaternary ZAGO thin films on sapphire substrates, achieved through thermal annealing of a ZnGa2O4 (ZGO) epilayer on sapphire in an ambient air setting. In-situ annealing x-ray diffraction measurements show that the incorporation of Al in the ZGO epilayer commenced at 850 °C. The Al content (x) in ZAGO epilayer gradually increased up to around 0.45 as the annealing temperature was raised to 1100 °C, which was confirmed by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy. X-ray rocking curve measurement revealed a small full width at half maximum value of 0.72 °, indicating the crystal quality preservation of the ZAGO epilayer with a high Al content. However, an epitaxial intermediate �–(AlxGa1−x)2O3 layer (� - AGO) was formed between the ZAGO and sapphire substrate. This is believed to be a consequence of the interdiffusion of Al and Ga between the ZGO thin film and sapphire substrate. Using density functional theory, the substitution cost of Ga in sapphire was determined to be about 0.5 eV lower than substitution cost of Al in ZGO. Motivated by this energetically favorable substitution, a formation mechanism of the ZAGO and AGO layers was proposed. Spectroscopic ellipsometry studies revealed an increase in total thickness of the film from 105.07 nm (ZGO) to 147.97 nm (ZAGO/AGO) after annealing to 1100 °C, which were corroborated using TEM. Furthermore, an observed increase in the direct (indirect) optical bandgap from 5.06 eV (4.7 eV) to 5.72 eV (5.45 eV) with an increasing Al content in the ZAGO layer further underpins the formation of a quaternary ZAGO alloy with a tunable composition.
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| 3. |
- Horng, Ray-Hua, et al.
(författare)
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Growth and Characterization of Sputtered InAlN Nanorods on Sapphire Substrates for Acetone Gas Sensing
- 2024
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- The demand for highly sensitive and selective gas sensors has been steadily increasing, driven by applications in various fields such as environmental monitoring, healthcare, and industrial safety. In this context, ternary alloy indium aluminum nitride (InAlN) semiconductors have emerged as a promising material for gas sensing due to their unique properties and tunable material characteristics. This work focuses on the fabrication and characterization of InAlN nanorods grown on sapphire substrates using an ultra-high vacuum magnetron sputter epitaxy with precise control over indium composition and explores their potential for acetone-gas-sensing applications. Various characterization techniques, including XRD, SEM, and TEM, demonstrate the structural and morphological insights of InAlN nanorods, making them suitable for gas-sensing applications. To evaluate the gas-sensing performance of the InAlN nanorods, acetone was chosen as a target analyte due to its relevance in medical diagnostics and industrial processes. The results reveal that the InAlN nanorods exhibit a remarkable sensor response of 2.33% at 600 ppm acetone gas concentration at an operating temperature of 350 degrees C, with a rapid response time of 18 s. Their high sensor response and rapid response make InAlN a viable candidate for use in medical diagnostics, industrial safety, and environmental monitoring.
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| 4. |
- Horng, Ray-Hua, et al.
(författare)
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Structure Effect on the Response of ZnGa2O4 Gas Sensor for Nitric Oxide Applications
- 2022
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 12:21
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Tidskriftsartikel (refereegranskat)abstract
- We fabricated a gas sensor with a wide-bandgap ZnGa2O4 (ZGO) epilayer grown on a sapphire substrate by metalorganic chemical vapor deposition. The ZGO presented (111), (222) and (333) phases demonstrated by an X-ray diffraction system. The related material characteristics were also measured by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. This ZGO gas sensor was used to detect nitric oxide (NO) in the parts-per-billion range. In this study, the structure effect on the response of the NO gas sensor was studied by altering the sensor dimensions. Two approaches were adopted to prove the dimension effect on the sensing mechanism. In the first approach, the sensing area of the sensors was kept constant while both channel length (L) and width (W) were varied with designed dimensions (L x W) of 60 x 200, 80 x 150, and 120 x100 mu m(2). In the second, the dimensions of the sensing area were altered (60, 40, and 20 mu m) with W kept constant. The performance of the sensors was studied with varying gas concentrations in the range of 500 ppb similar to 10 ppm. The sensor with dimensions of 20 x 200 mu m(2) exhibited a high response of 11.647 in 10 ppm, and 1.05 in 10 ppb for NO gas. The sensor with a longer width and shorter channel length exhibited the best response. The sensing mechanism was provided to explain the above phenomena. Furthermore, the reaction between NO and the sensor surface was simulated by O exposure of the ZGO surface in air and calculated by first principles.
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| 5. |
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| 6. |
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| 7. |
- Hsu, Yu-Hsuan, et al.
(författare)
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epsilon-Ga2O3 Grown on c-Plane Sapphire by MOCVD with a Multistep Growth Process
- 2022
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Ingår i: Crystal Growth & Design. - : AMER CHEMICAL SOC. - 1528-7483 .- 1528-7505. ; 22:3
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Tidskriftsartikel (refereegranskat)abstract
- Gallium oxide (Ga2O3) has especially become popular because of its established applications in semiconductors. Of five polymorphs, monoclinic beta-Ga2O3 is the most thermodynamically stable phase. However, orthorhombic Ga2O3 (also known as epsilon-Ga2O3 or kappa-Ga2O3) is gaining increasing interest due to its high lattice symmetry and peculiar ferroelectricity. Although the structural approach for estimating Ga2O3 has been studied both theoretically and experimentally, epsilon-Ga2O3 and kappa-Ga2O3 are still confused. In this study, epsilon-Ga2O3 epilayers are grown on c-plane sapphire by metal-organic chemical vapor deposition with a multistep growth process. A thin annealed epsilon-Ga2O3 buffer layer is grown in the first step. The sequent growth steps with slow, fast, or combination of slow then fast growth rate significantly influence the quality of epilayers compared with that of directly grown Ga2O3. Through a detailed transmission electron microscopy (TEM) characterization of these Ga2O3 epilayers, the structural relationship between orthorhombic kappa-Ga2O3 and hexagonal epsilon-Ga2O3 is elucidated. A series of first-principles density functional theory calculations are also carried out to confirm the argument.
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| 8. |
- Lin, Lien-Hsuan, et al.
(författare)
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HYDRODYNAMICAL SIMULATIONS OF THE BARRED SPIRAL GALAXY NGC 1097
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X. ; 771:1
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Tidskriftsartikel (refereegranskat)abstract
- NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable, which is consistent with the observation in Hsieh et al. Our simulations show that the gas inflow rate is 0.17 M-circle dot yr(-1) into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.
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| 9. |
- Lin, Shao-Hua, et al.
(författare)
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Study on different isolation technology on the performance of blue micro-LEDs array applications
- 2024
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Ingår i: DISCOVER NANO. - : SPRINGER. - 2731-9229. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a 3 x 3 blue micro-LED array with a pixel size of 10 x 10 mu m2 and a pitch of 15 mu m was fabricated on an epilayer grown on a sapphire substrate using metalorganic chemical vapor deposition technology. The fabrication process involved photolithography, wet and dry etching, E-beam evaporation, and ion implantation technology. Arsenic multi-energy implantation was utilized to replace the mesa etching for electrical isolation, where the implantation depth increased with the average energy. Different ion depth profiles had varying effects on electrical properties, such as forward current and leakage currents, potentially causing damage to the n-GaN layer and increasing the series resistance of the LEDs. As the implantation depth increased, the light output power and peak external quantum efficiency of the LEDs also increased, improving from 5.33 to 9.82%. However, the efficiency droop also increased from 46.3 to 48.6%.
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| 10. |
- Lu, Chan-Hung, et al.
(författare)
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beta-Ga2O3 MOSFETs electrical characteristic study of various etching depths grown on sapphire substrate by MOCVD
- 2023
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Ingår i: DISCOVER NANO. - : SPRINGER. - 2731-9229. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- beta-Ga2O3 thin films with both a 45 nm Si-doped conductive epilayer and unintentionally doped epilayer were grown on c-plane sapphire substrate by metalorganic chemical vapor deposition. beta-Ga2O3 based metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with gate recess depths of 20 nm and 40 nm (it indicated gate depth with 70 nm and 50 nm, respective), respectively, and without said recessing process. The conductivity of beta-Ga2O3 epilayers was improved through low in situ doping using a tetraethoxysilane precursor to increase MOSFET forward current density. After recessing, MOSFET operation was transferred from depletion to enhanced mode. In this study, the maximum breakdown voltage of the recessed 40 nm transistor was 770 V. The etching depth of a recessed-gate device demonstrates its influence on device electrical performance.
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