Papers by Keyword: Gallium Oxide

Abstract: In addition to silicon carbide (SiC) and gallium nitride (GaN), gallium oxide (Ga₂O₃) is attracting attention as a widegap semiconductor material. Ga₂O₃, unlike SiC and GaN, is not as hard, but has strong cleavage properties, making highly effective mechanical machining difficult. Thus, the processing of Ga₂O₃ by high-speed etching employing atmospheric-pressure plasma was studied. An extremely high removal rate of 60 μm/min was obtained due to basic processing experiments using hydrogen gas instead of toxic and corrosive chlorine gas as the reaction gas.

Abstract: Gallium oxide (β-Ga₂O₃) nanostructures (NSs) have been successfully obtained through a simple scalable synthesis via thermal evaporation of gallium (III) oxide powder in hydrogen-ambient chemical vapour deposition (HACVD) without the presence of carrier gas. β-Ga₂O₃ was deposited on Si substrate by evaporating the source material at 1000 C in a regulated hydrogen reducing atmosphere, for 120 min growth time. Hydrogen ambient was regulated by varying the flow to observed changes in the morphological, structural and optical properties of films. The samples were characterized using high resolution X-ray diffraction (HR-XRD), field-emission scanning electron microscope (FE-SEM) and UV-vis-NIR spectrophotometer. The density and quality of NSs was observed to increase with hydrogen gas supply. The rarely reported 1) dominant XRD peak of β-Ga₂O₃ was obtained in the event of eliminating the carrier gas which is part of the usual recipe for CVD technique. The average crystallite size and energy gap of the synthesized material was found to decrease with increased hydrogen flow rate from 176.5 to 39.8 nm and 5.47 to 4.83 eV, respectively.

Abstract: Gallium oxide nanowires were grown on different substrates using a corona plasma assisted vapor phase epitaxy process and gold catalyst. It is shown that the silicon carbide pseudo substrate in combination with the plasma excitation of the gas phase supports the growth of the gallium oxide nanowires. Analyzing the orientation of the nanowires with respect to the growth surface, it is concluded that the nanowires growth proceed along the fast growth direction of gallium oxide.

Abstract: Growth of gallium oxide thin film was realized with MOCVD on (0001) sapphire substrate. Structural and compositional properties of thin film were studied employing trimethylgallium and water as precursors, carrier gases were H₂ and N₂. Obtained film is polycrystalline and predominantly consisted of (201) oriented β-Ga₂O₃. Sample exhibited blue luminescence which is attributed to oxygen vacancies. H₂ gas proved to have beneficial effect on film quality and overall growth process.

Abstract: GaN epitaxial layers were successfully grown by hydride vapour phase epitaxy (HVPE) on β-Ga₂O₃ substrates produced by cleaving. The initial stages of GaN epitaxial growth on β-Ga₂O₃ were studied by scanning electron microscopy (SEM) and x-ray diffraction analysis (XRD). The nucleation and the transition from the nucleation layer to a continuous GaN film were studied. It was found that the growth starts with formation of small crystallites on the substrate surface. As the growth continues, crystallites transform into pyramidal islands which increase in size and merge together. It was found that the structural quality of the GaN layers rapidly improves with increasing thickness. The full width at half maximum of x-ray ω rocking curves for (0002) peak decreased from 1370 to 540 arcsec as the deposition time was increased from 30 to 120 sec. This corresponds to the variation of the nominal layer thickness from 250 nm to 1000 nm.

Abstract: Effects of a metal oxide structure on the oxygen sensing properties are investigated. In the existence of the etched V-groove gallium oxide geometry, its electrical and sensing properties, i.e., high sensitivity and response time areinvestigated. Grain sizes of the material are dependent on different sputtering conditions and investigated by AFM. Under the partial-voltage circuit measurement, it can be confirmed that the increase of temperature will result in the increase of resistance for the Ga₂O₃ oxygen sensor. From experiment, good stability and repeatability of the oxide sensor are demonstrated when tested under oxygen concentration. These properties show that the oxide structure has a good potential for high sensitivity oxygen sensor.

Abstract: Sn-doped monoclinic β-Ga₂O₃ nanoparticles were successfully fabricated on Si (111) substrates with NiCl₂ as a catalyst by chemical vapor deposition using metallic gallium and oxygen as sources. The composition, crystal structure, morphology, and optical properties were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectrophotometry (FTIR), and photoluminescence, respectively. The results demonstrate that the sample was monoclinic β-Ga₂O₃ nanoparticles with diameters approximately ranging from 200~300 nm. Well-defined prominent absorption bands located at 458 and 671 cm^-1 in the FTIR spectra corresponded to Ga-O vibrations. The photoluminescence spectrum shows that the Ga₂O₃ nanoparticles have a broad and strong emission band ranging from 300 nm to 650 nm with four Gaussian bands centered at approximately 346 (UV), 416 (blue), 473 (dark blue), and 529 nm (green), which may be attributed to defects such as oxygen vacancies and galliumoxygen vacancy pairs. The growth mechanism of β-Ga₂O₃ nanoparticles is discussed in brief.

Abstract: For the purpose of increasing the conductivity of β-Ga₂O₃ films, Sn doping in the β-Ga₂O₃ films has been explored using co-sputtering. Growth of β-Ga₂O₃ was confirmed by the XRD pattern for the undoped sample. However, it is shown that the Ga₂O₃ phase is transformed from the β to the γ phase by Sn doping, because of the increase of the phase transition temperature from the γ to the β phase. To improve the crystalline quality, additional annealing at 900°C for 60 min is performed to the Sn doped film. The XRD peaks corresponding with β-Ga₂O₃ could be confirmed after the additional annealing.

Abstract: For the purpose of improving the crystalline quality of undoped and Si doped β-Ga₂O₃ films, high temperature annealing at 900°C was performed. The crystalline quality of the films investigated using scanning electron microscopy and X-ray diffraction. Also the conductivity of the films is compared before and after the annealing. After the 900°C annealing, the XRD peaks intensity corresponding to β-Ga₂O₃ is increased. This result indicates that the crystalline quality improves by the high temperature annealing.

Abstract: High resolution X-ray photoelectron spectroscopy (XPS) is used to investigate the spectra of nanolayered films. Amorphous gallium oxide (Ga2O3)-silicon dioxide (SiO2) nanolayered thin films are grown using ultrahigh vacuum radio frequency (rf) magnetron sputtering on sapphire substrates at room temperature. Films are layered with 15-angstrom Ga2O3 oxide and 75-angstrom SiO2 for a total of 10 layers. Referring to atomic core levels, atomic contribution to valence band density of states is experimentally nominated. This analytical technique has particular applicability to the evaluation of the density of states with atomic contributions.