Ga2O3 Powder Research Articles

Reaction-sintered highly transparent MgGa2O4 ceramics with enhanced dielectric properties

Reaction sintering of MgO and Ga2O3 powders was first used to prepare MgGa2O4 transparent ceramics. The microstructural evolution suggested that the negligible volume change resulting from the solid-phase reaction of MgO and Ga2O3, as well as the close and homogeneous arrangement of both fine particles, are the key factors in obtaining pre-sintered ceramics with an ideal microstructure at lower temperature. After a hot isostatic pressing (HIP) treatment, the fully dense ceramic exhibited improved in-transmittance (74.7 %@600 nm, and 85.4 %@4401 nm) and quality factor (Q × f = 168,000 GHz). Due to the combination of high transparency, wide transmission range (6.22 μm at the 60 % transmittance), ultra-low dielectric loss, and near-zero temperature coefficient of resonance frequency (− 3.9 ppm/°C), transparent MgGa2O4 ceramic is suggested to be an ideal optical-dielectric integration material.

Investigations of the growth and physical characteristics of ZNF2-DOPED GA2O3 thin films

This study began by preparing gallium oxide (Ga2O3) doped with zinc fluoride (ZnF2) and manufacturing a target material. Subsequently, electron beam (e-beam) deposition was employed to coat silicon substrates with the prepared material. Different heat treatment conditions were applied to the deposited films, followed by material and electrical property analyses. The investigation explored the impact of pre-sintering Ga2O3 at 950°C to transform it into a more stable [Formula: see text]-phase. For comparative purposes, some samples underwent annealing at 600°C in a nitrogen–hydrogen (95% N[Formula: see text] H2, abbreviated as N[Formula: see text]) mixed gas, which was used as a reduction atmosphere, to increase oxygen vacancies in the ZnF2-doped Ga2O3 thin films and consequently enhance their conductivity. The deposited ZnF2-doped Ga2O3 thin films initially exhibited an amorphous phase, with diffraction peaks appearing only after a 600°C annealing process. Pre-sintering Ga2O3 powder at 950°C promoted the emergence of the [Formula: see text]-phase, and the bandgap value increased after annealing. Measurements using B1500A revealed that sintering and annealing ZnF2-doped Ga2O3 thin films were essential steps to enhance their conductivity. X-ray photoelectron spectroscopy (XPS) further confirmed a significant correlation between the conductivity variation and the concentration of oxygen vacancies. Additionally, it was observed that the use of an N[Formula: see text] mixed gas further increased the presence of oxygen vacancies in the films. The results of this study provide an important method to make Ga2O3 thin films with conductivity, which can be utilized in the fabrication of Ga2O3 thin-film-based semiconductor devices in the future.

Influence of particle size distribution on dielectric, electrical, and microstructural properties of aerosol-deposited Ga2O3 film for advanced electronic device

Gallium oxide (Ga2O3) films have been the subject of recent scientific and technological research, owing to their outstanding characteristics. In this study, a rapid and efficient aerosol deposition (AD) process was utilized to produce Ga2O3 films. The effect of the particle size distribution (PSD) of the columnar or plate-like Ga2O3 starting powder on the dielectric, electrical, and microstructural properties of the films was also investigated. The dielectric constant and loss tangent of polycrystalline β-Ga2O3 films fabricated using AD with narrow PSD Ga2O3 powder were 10 and 6.7% at 10 kHz, respectively. In contrast, the films composed of a wide PSD powder exhibited a dielectric constant of 18 and a loss tangent of 3.6%. The leakage current densities of 1.77 × 10−5 and 6.63 × 10−7 A/cm2 at 5 V of the films using narrow and wide PSD powder were observed, respectively. In addition, the breakdown electric fields of the Ga2O3 films with narrow and wide PSD powder were 1.15 and 1.06 MV/cm, respectively. Qualitative and quantitative analyses of the surface and inner microstructure were conducted to elucidate the differences in film characteristics according to the PSD. Consequently, a wider PSD enables the production of relatively denser and flatter high-quality films owing to enhanced hammering and crush effects. These results suggest potential applications of Ga2O3 films fabricated using AD in various fields, such as capacitors, power semiconductors, and sensor devices.

(Digital Presentation) Electrochemical Properties of Ta-Doped Li7La3Zr2O12 Ceramic Electrolyte Sintered with Ga2O3 Additive

A garnet-type oxide with the formula of Li7La3Zr2O12 (LLZO) has attracted much attention because of its high Li ion conductivity at room temperature, excellent thermal performance, and high stability against Li metal.1,2) However, poor interfacial connection causes non-uniform Li plating and intergranular penetration of Li dendrite in polycrystalline LLZO when the cell is cycled particularly at high current densities, resulting in internal short-circuit failure.3,4) It has been pointed out that the tolerance for Li dendrite growth into LLZO is influenced by many factors such as the interfacial resistance between LLZO and Li anode, cell stacking pressure and microstructure (density and grain size) of LLZO. In this study, we fabricated Ta-doped LLZO (Li6.55La3Zr1.55Ta0.45O12) solid electrolytes with Ga2O3 additive and investigated the effects on the microstructure and electrochemical properties.Ta-doped LLZO with Ga2O3 additive were synthesized via a conventional solid-state reaction process. 1-7 mol % Ga2O3 powder was mixed with calcined Ta-doped LLZO powder. The mixture was pelletized and then sintered at different temperatures with an Al-free crucible. In XRD analysis, each sintered sample has a cubic garnet phase and diffraction peaks from other phases were not detected. In SEM observation, microstructure of sintered sample was strongly influenced by sintering temperature and Ga2O3 addition, due to the sintering with liquid Li-Ga-O phase during high temperature sintering.5, 6) The high total (bulk + grain-boundary) ionic conductivity above 1 mS cm-1 at room temperature was obtained in samples composed of large grains with the size of several 10 to 100 µm. However, the tolerance for Li dendrite growth characterized in a symmetric cell is improved remarkably in the samples with uniform microstructure composed of fine grains with the size of below 5 µm. Since the interfacial resistance between Li and solid electrolyte was adjusted to the same level, the difference in tolerance for Li dendrite growth is mainly attributed to the difference in microstructure depending on both the sintering condition and the amounts of Ga2O3 addition.

Fabrication of UV-C photodetector with ultimate stability in extreme space environments (radiation, low temperature) using aerosol-deposited Ga2O3

We report on the fabrication and characterization of a Ga2O3-based UV-C photodetector using the aerosol deposition (AD) method. By optimizing the size and crystallinity of the Ga2O3 powder, we were able to obtain a uniform thin film with high transmittance (70–80%) without the need for additional heat treatment or high vacuum environments. The resulting Ga2O3 film exhibited a high and selective response to 254 nm wavelength light, even without any treatment, and remained stable when exposed to γ-radiation. The photodetector also performed well in extreme temperatures (−196 °C–150 °C), making it suitable for use in harsh environments, such as the space industry. Our findings demonstrate the potential of the AD method for the fabrication of high-quality Ga2O3 thin films for photodetector applications.

Investigation of β-Ga2O3 thick films grown on c-plane sapphire via carbothermal reduction

We investigated the influence of the growth temperature, O2 flow, molar ratio between Ga2O3 powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire (0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga2O3 illustrate that β-Ga2O3 growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga2O3 films was produced when the O2 flow was 20 sccm. To guarantee that β-Ga2O3 films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga2O3 powder should be set at 10 : 1.

Structural and Scintillation Properties of Ce3+:Gd3Al3Ga2O12 Translucent Ceramics Prepared by One-Step Sintering.

Cerium-doped gadolinium aluminum gallium garnet (Ce3+:Gd3Al3Ga2O12, Ce3+:GAGG) ceramic is a promising scintillation material. In this study, Ce3+:Gd3Al3Ga2O12 scintillation ceramics were prepared by the one-step sintering of commercially available Gd2O3, Al2O3, Ga2O3, and CeO2 powders in a flowing oxygen atmosphere at 1600 °C by solid-phase reaction sintering. For all the Ce3+:Gd3Al3Ga2O12 ceramic samples doped with different amounts of Ce3+ doping, dense ceramics were obtained. The structure, photoluminescence, and scintillation properties of the Ce3+:Gd3Al3Ga2O12 ceramics have been investigated. The average grain size of samples sintered at 1600 °C is about 2 μm. The X-ray excitation luminescence peak is around 560 nm, which is consistent with that of Ce3+:Gd3Al3Ga2O12 single crystals, matching well with the computed tomography X-ray detector's response sensitivity. The light yield is higher compared to the standard reference sample-lutetium yttrium orthosilicate single crystal.

Structural, chemical network and optoelectronic properties of Ag catalyzed CVD grown gallium nitride nanowires in reduced atmosphere

Silver catalyst-mediated Gallium Nitride Nanowires (Ag-GNNWs) were synthesized on Si (100) substrate taking Ga2O3 powder, N2 and H2 gas as raw material using a chemical vapor deposition (CVD) reactor. The structural, chemical network and optoelectronic environment of Ag-GNNWs were investigated by employing AFM, FTIR, Raman, XRD, Photoluminescence (PL), and XPS characterization with the variation of H2 flow rate. The AFM and XRD results confirmed that the diameters and crystallite size, D of Ag-GNNWs varied from 50 to 250 nm and 15.06 nm respectively. The microstrain of Ag-GNNWs varied from 0.00174 to 0.01183 with an increase of H2 gas reduced atmosphere. The FTIR signatures at 463, 514, 567, 610, 667 and 739 cm−1 correspond to H-Ga-O, N-Ga-N, N-Ga-O, O-Ga-O(GaOO), O-Ga = O(O-Ga = O) and A1(LO) phonon respectively indicated Oxygen present as contamination. The increase in FWHM of Raman spectra signified decreased phonon lifetime of the transverse optic (A1 & E1), surface optic (A & E), E2(High) and defect-induced phonon with increasing H2 gas flow rate. The ISO(A) / ISO(E) and its respective FWHM ratio increased from 1.22 to 1.49 and 1.09 to 1.30 cm−1, indicating decreasing structural anisotropy and crystalline quality with the variation of H2 flow rate. The prominent PL peak centered at around 2.97 eV implied nitrogen-vacancy (VN) in the Ag-GNNWs. The XPS spectrum confirmed the presence of Ga, Ag, N2 and O are present in Ag-GNNWs. Moreover, semiempirical deconvolution predicts possible chemical networks in the Ag-GNNWs.

Study of NiGa2O4 microneedles grown by a thermal-evaporation method

NiGa2O4 microneedles with variable morphology and dimensions were synthesized by an autocatalytic Vapor-Liquid-Solid process using Ga2O3, metallic Ga and Ni precursor powders. The resulting structures exhibit {100} crystallographic facets and different inversion degrees of the spinel structure owing to the diverse temperatures employed during the synthesis. Advantage was taken of the high crystallinity and preferred orientation of the structures to study and assign the Raman vibrational modes. Photoluminescence measurements reveals defect-related and near-bandgap emissions in the probed microstructures. The growth process and the physical mechanisms involved were also discussed.

The Fabrication of Indium–Gallium–Zinc Oxide Sputtering Targets with Various Gallium Contents and Their Applications to Top-Gate Thin-Film Transistors

We prepared amorphous indium–gallium–zinc oxide (a-IGZO) thin films with various Ga content ratios and investigated their feasibility as the active channel layers of top-gate thin-film transistors (TFT). First, the 2-inch IGZO sputtering targets with stoichiometric ratios of InGaZn2O5, InGaZnO4, and InGa2ZnO5.5 were fabricated using In2O3, Ga2O3, and ZnO oxide powders as raw materials via sintering treatments at temperatures ranging from 900 °C to 1300 °C for 6 h or 8 h. X-ray diffraction analysis indicated that the InGaZn2O5 and InGaZnO4 targets are single-phase structures whereas the InGa2ZnO5.5 target is a two-phase structure. Hall effect measurement indicated that the a-InGaZn2O5 and a-InGaZnO4 layers possess a carrier concentration (N) of about 1019 cm−3 and a resistivity (ρ) of about 10−2 Ω·cm; however, the N of the a-InGa2ZnO5.5 layer is only 1017 cm−3, and the ρ is about 1 to 4 Ω·cm. Moreover, the a-InGaZn2O5 layer exhibited the highest Hall-effect mobility (μHall) of 21.17 cm2·V−1·sec−1. This indicated that the impedance of Ga3+ ions to carrier migration is the main factor affecting the electrical properties of a-IGZO layers. Ga content in the a-IGZO channel similarly affects the performance of the TFT devices prepared in this study. The annealing at 300 °C for 1 h in an ambient atmosphere was found to significantly improve the electrical properties of the TFT devices. The best performance was observed in the a-InGaZnO4 TFT sample subjected to post-annealing at 300 °C with Vth = −0.85 V, μFE = 8.46 cm2, V−1·sec−1, SS = 2.31, V·decade−1, and Ion/Ioff = 2.9 × 104.

Phases transition, component variation and valence of Tb element during terbium gallium garnet polycrystalline synthesization

Terbium gallium garnet (Tb3GaxO12, TGG) is an excellent magneto-optical material and widely used in magneto-optical isolators of laser systems, it is an important topic to grow large-size and high-quality single crystal. It was found that the TGG polycrystalline reacting completely was very important for good-quality single crystal growth. However, the phases transitions, Ga component volatilization and the valence of Tb element during synthesizing TGG polycrystalline with Tb4O7 and Ga2O3 were not been reported previously. In this work, the commercial Ga2O3 powder and Tb4O7 were selected as starting raw materials, and the samples with various initial chemical stoichiometric ratios were calcined at the different temperatures. The phases transition was semi-quantitatively investigated with X-ray diffraction (XRD) and Rietveld refinement. Some of the Ga2O3 from the starting material and Tb2O3 formed at high temperature gradually disappeared at no more than 1100°C. The tri-terbium gallate dioxide (TGD) was found as a metastable phase, which disappeared at no more than 1200°C. The chemical stoichiometric ratios change and Ga element loss were investigated with X-ray fluorescence (XRF) analysis and found that loss rate of Ga element is close to 23% after calcined at 1200°C or higher temperatures for 48 ​h. The X-ray photoelectron spectroscopy (XPS) analysis shows that there is no or little Tb4+ ion existed in samples after being calcined at or above 900°C. In summary, the appropriate initial molar ratio range for synthesizing pure TGG polycrystalline is Tb: Ga ​= ​3 : 4.75–5.15, and the best calcination temperature is 1200°C.

Electrophysical properties of ITO:Ga2O3 films grown by rf magnetron sputtering

n this paper, the electrophysical properties of ITO:Ga2O3 thin films grown by RF magnetron sputtering on glass and sapphire substrates are studied. Targets prepared by mechanical pressing of ITO and Ga2O3 powders are used as an evaporation source. The electrophysical characteristics as a function of optimumfilm growth parameters—the correlation between the argon and oxygen flows, the substrate temperature, and the discharge power of the magnetron—are studied

Fabrication, Characterization and Performance of Low Power Gas Sensors Based on (GaxIn1-x)2O3Nanowires.

Active research in nanostructured materials aims to explore new paths for improving electronic device characteristics. In the field of gas sensors, those based on metal oxide single nanowires exhibit excellent sensitivity and can operate at extremely low power consumption, making them a highly promising candidate for a novel generation of portable devices. The mix of two different metal oxides on the same nanowire can further broaden the response of this kind of gas sensor, thus widening the range of detectable gases, without compromising the properties related to the active region miniaturization. In this paper, a first study on the synthesis, characterization and gas sensing performance of (GaxIn1-x)2O3 nanowires (NWs) is reported. Carbothermal metal-assisted chemical vapor deposition was carried out with different mixtures of Ga2O3, In2O3 and graphite powders. Structural characterization of the NWs revealed that they have a crystalline structure close to that of In2O3 nanowires, with a small amount of Ga incorporation, which highly depends on the mass ratio between the two precursors. Dedicated gas nanosensors based on single NWs were fabricated and tested for both ethanol and nitrogen dioxide, demonstrating an improved performance compared to similar devices based on pure In2O3 or Ga2O3 NWs.

Low-temperature sintering of highly conductive ZnO:Ga:Cl ceramics by means of chemical vapor transport

A new technology for sintering a ZnO + Ga2O3 powder via chemical vapor transport based on HCl has been developed. The proposed sintering method has the following advantages: a low sintering temperature of 1000–1100 °C, there is no need to use of expensive dopant nanopowders, the possibility of multiple re-sintering, and the absence of changes in the diameter of the ceramics after sintering. A ZnO:Ga:Cl ceramics with a density of 5.31 g/cm3, a hardness of 2.0 GPa, and a resistivity of 1.46 × 10–3 Ω⋅cm has been synthesized. The solubility limit of the Ga2O3 dopant has been estimated at about 3 mol %. At a higher doping level, the content of the ZnGa2O4 spinel phase becomes significant. In addition, ZnO:Ga:Cl thin films with a resistivity of 2.77 × 10–4 Ω⋅cm can be grown by DC magnetron sputtering of the synthesized ceramics.

Crystallite size and micro-strain investigations of hydrothermally synthesized β-Ga2O3 by different analytical methods

XRD pattern of [Formula: see text]-Ga2O3 powder, synthesized through template-free two step hydrothermal method at low temperature thoroughly, is investigated by imposing different methods of analysis. Both crystallite sizes and micro-strains of the micro-structures are analyzed and compared. Along with the traditional Scherrer’s formula (S-average, LF and LFTZ), modified Williamson–Hall (W-H) method with UDM, USDM and UDEDM and Size-Strain Plot (SSP) method were used for the investigation. Stress and defect energy densities were calculated from USDM and UDEDM modified W-H plots of the powder sample, respectively. Detailed analysis of the crystallite size and micro-strain from different methods/models was done. Obtained crystallite sizes and micro-strains from different models were compared with the results obtained from TEM analysis. It was found that crystallite sizes obtained from UDM modified W-H analysis and SSP models well coincided with crystallite size observed from TEM micrograph.

Mechanical alloying of Ga2O3 and Ga2O3-Al2O3

Mechanical milling of Ga2O3 powder and a mixture of Ga2O3 and Al2O3 was performed with the intent to prepare a (AlGa)2O3 alloy. Vibrational milling was conducted with stainless steel or zirconia ceramic balls. The milled samples were characterized using X-ray diffraction (XRD) analysis, Raman spectroscopy, and microscopic observation. During the mechanical milling of Ga2O3, the monoclinic β-Ga2O3 phase was transformed into the corundum α-Ga2O3 phase, and the phase transition was presumed to be similar to that induced by pressure loading. The fraction of α-Ga2O3 phase increased with milling time in a manner consistent with the Johnson–Mehl–Avrami (JMA) equation. Mechanical alloying of the Al2O3-Ga2O3 system was performed for 1200 h. Although the XRD and Raman peaks for both α-Al2O3 and α-Ga2O3 were broadened with increasing alloying time, and some of the peaks gradually merged, no distinct evidence of the production of single-phase (Al0.5Ga0.5)2O3 was obtained. It is thus difficult to synthesize the (Al0.5Ga0.5)2O3 phase by powder metallurgy methods.

Growth of GaN layers using Ga2O vapor synthesized from Ga2O3 and carbon

Abstract In this study, we grew GaN layers using Ga2O vapor synthesized from Ga2O3 powder and carbon powder. To precisely regulate the growth rate of the GaN layers, we controlled the supply rate of Ga2O vapor by controlling the reaction rate between Ga2O3 and carbon. The results showed that the growth rate increased linearly with partial pressure of Ga2O vapor and that GaN layers with the smooth (0 0 0 1) surface could be grown at 10–49 μm/h. X-ray diffraction (XRD) measurements revealed that the epitaxial layer was single-crystalline GaN and the FWHM of the GaN epitaxial layers ranged from 51 to 105 arcsec, confirming that the epitaxial layers inherit the high crystallinity of the seed substrates. Secondary ion mass spectrometry (SIMS) analysis showed that the oxygen concentrations in the epitaxial layers at the growth rates of 15 and 49 μm/h were 2.0 × 1017 and 2.5 × 1019 atoms/cm3, respectively. The carbon concentration in the epitaxial layers was below the detection limit. These values were the lowest seen in crystals obtained by the conventional technique using Ga2O vapor. These results show that this method, using Ga2O vapor produced by the reaction of Ga2O3 with carbon, has the potential to grow GaN crystals with high crystallinity and high purity by promoting the smoothness of the (0 0 0 1) surface.

Influence of Zn doping on the morphology and luminescence of Ga2O3 low-dimensional nanostructures

Zn-doped Ga2O3 nanostructures were synthesized by thermal evaporation. SEM results show that there are plenty of nanorods in the samples. The EDS analysis of the samples demonstrate that the nanostructures are mainly composed of Ga and O elements, and a small amount of Zn element is also observed. The Raman spectra indicate that the samples still keep the monoclinic structure consistent with the pure Ga2O3 crystal structure. A broad-band blue-green luminescence centered around at 2.3 eV was observed at room temperature. The luminescence intensity of the PL spectra of the Zn-doped Ga2O3 nanostructures varied with the amount of Zn doping. Besides, the PL spectra of the Zn-doped Ga2O3 nanostructures have a red-shift compared to that of the pure Ga2O3 nanostructures. The analysis of the PL spectrum of Zn-doped Ga2O3 nanostructures with a mass ratio of Ga2O3 powder to zinc powder of 10:1 indicates that the broad-band blue-green luminescence of the Zn-doped Ga2O3 nanostructures is composed of one blue luminescence (2.8 eV, 450 nm) band, one green luminescence (2.3 eV, 533 nm) band, one yellow luminescence (2.1 eV, 592 nm) band, and one red luminescence (1.9 eV, 638 nm) band, respectively. Further, their luminescence mechanisms will be discussed.

Microstructure and phase transformation of IGZO targets with different stoichiometry during sintering

In this study, indium-gallium-zinc oxide (IGZO) target was synthesized through a pressureless oxygen atmosphere sintering technique, and the effects of chemical stoichiometry and sintering temperature on the IGZO ceramic targets were systematically studied. In2O3, Ga2O3, and ZnO powders in the mole ratio of 1:1:1 and 1:1:4, respectively, were selected as raw materials. After ball milling, green compacts were obtained by granulation and isostatic pressing technology. Then the green compacts were sintered at different temperatures under oxygen atmosphere. The microstructure and phase compositions of the IGZO ceramic targets were analyzed by scanning electron microscopy and X-ray diffraction. In2O3 and ZnGa2O4 phases were observed for the IGZO-111 ceramic at temperatures below 1300 °C. However, single phase of InGaZn2O5 was generated at 1204 °C for the IGZO-114 ceramics and no phase transformation occurred between 1300 and 1500 °C. The IGZO-111 ceramic with lower Zn content was easier to densify; nonetheless, the reaction process was delayed throughout the temperature range. However, the IGZO-114 ceramic with high Zn content exhibited a faster reaction process, but the densification was slower. The IGZO-111 ceramics showed a smaller resistivity of 3.4 mΩ cm at 1500 °C compared to IGZO-114 ceramics. The perfect microstructure and generation of In2Ga2ZnO7 phase with lower resistivity in the IGZO-111 ceramics contributed to better electrical performance of the IGZO targets.

Study on the IGZO Ceramics Sintered at Different Temperatures

In this study, the IGZO target was synthesized through a pressureless oxygen atmosphere sintering technique, and the effects of sintering temperature on IGZO ceramic target were studied. The In2O3, Ga2O3 and ZnO powders in the mole ratio of 1:1:2 were selected as raw materials. The powders were mixed by ball milling, and then the granulation and pressing process were used in order to obtain the green compacts. Then the green compacts were sintered at different temperature under oxygen atmosphere. The microstructure characterizations and compositions of the IGZO ceramic targets were analyzed. The results indicated that the lower sintering temperature was beneficial for IGZO ceramics to form the regular polygonal grains. With the temperature increased, the densification of IGZO ceramics was highly activated, and the low porosity was obtained. The XRD results demonstrated that the single phase of InGaZnO4 had been generated at 1100°C and no phase transformation occurred between 1300°C and 1500 °C. However, the SEM results showed that the grain growth of IGZO target was very obvious at 1500°C. The IGZO ceramic had a highest relative density of 99.4% and optimal resistivity of 18 mΩ·cm at the sintering temperature of 1400°C.