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In this study, we successfully synthesized three gallium oxide thin films on (0001)-faceted Al 2 O 3 substrates using hydrogen-reduced chemical vapor deposition (CVD) at different deposition temperatures, resulting in distinct morphologies and crystalline phases. These films consist of two pure-phase β-Ga 2 O 3 films and one mixed-phase film comprising both β- and ε-Ga 2 O 3 phases. The mixed-phase samples were subsequently annealed at high temperatures to obtain pure-phase β-Ga 2 O 3 thin films. Furthermore, by precisely controlling the growth temperature, we achieved in-situ formation of Ga 2 O 3 nanostructures (nanowires and nanoribbons) on the surface of the β-Ga 2 O 3 thin films. The presence of different dominant crystal planes in the samples was confirmed through X-ray diffraction analysis (XRD) for verification purposes. In directly grown β-Ga 2 O 3 films, the (−201) plane emerged as the primary crystallographic plane, while both the (−201) and (401) planes dominated in β-Ga 2 O 3 films obtained via ε-Ga 2 O 3 film annealing. Raman spectroscopy findings further supported these observations regarding the crystalline phase of the films as observed through XRD analysis. Scanning electron microscopy (SEM) images revealed distinct film morphologies resulting from variations in deposition temperatures. A flatter surface was observed when a higher proportion of ε-Ga 2 O 3 was present in the film, however, regular cracking occurred after annealing. Atomic Force Microscope (AFM) images demonstrated that at a deposition temperature of 800 °C, regular steps were present on the film's surface. Mixed-phase films exhibited hillock morphology that disappeared after annealing, leading to a decrease in the surface roughness in root mean square (RMS) value. By elevating the growth temperature, a significantly enhanced density of gallium oxide nanoribbons can be seamlessly integrated onto the film surface. The transferred nanoribbons exhibit an ultra-thin profile with a minimum thickness of merely 12 nm, rendering them more slender and economically advantageous in comparison to conventional mechanical stripping methods. This study presents a CVD-based approach for growing gallium oxide thin films with varying morphologies by employing temperature modulation and demonstrates an innovative one-step method for growing nanostructures on gallium oxide films in situ, providing valuable insights for future device development involving gallium oxide. [ABSTRACT FROM AUTHOR]

In this study, the results of hydrogen plasma treatments of β-Ga2O3, α-Ga2O3, κ-Ga2O3 and γ-Ga2O3 polymorphs are analyzed. For all polymorphs, the results strongly suggest an interplay between donor-like hydrogen configurations and acceptor complexes formed by hydrogen with gallium vacancies. A strong anisotropy of hydrogen plasma effects in the most thermodynamically stable β-Ga2O3 are explained by its low-symmetry monoclinic crystal structure. For the metastable, α-, κ- and γ-polymorphs, it is shown that the net result of hydrogenation is often a strong increase in the density of centers supplying electrons in the near-surface regions. These centers are responsible for prominent, persistent photocapacitance and photocurrent effects. [ABSTRACT FROM AUTHOR]

The study of structural, morphological and photoluminescent properties of magnesium oxide, gallium trioxide nanopowders and their mixes obtained using pulsed laser reactive technology is carried out. The main emission peak for MgO located at about 430 nm can be assigned to recombination processes as a result of the formation of oxygen vacancy complexes. For Ga2O3 main emission band located at about 440 nm. Changing the gas environment (air, CO2, H2) leads to a significant change in the intensity of the spectra and its deformation for both metal oxides, that can be used in the gas sensors. The use of mixed metal oxides (MgO/Ga2O3) leads to improve sensitivity, enhanced adsorption ability, extensive catalytic activity, and high thermodynamic stability which is of considerable interest to the gas sensing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, GaxOyNz films were deposited onto p-Si (100) substrates by using electrodeposition technique under illumination. A mixture of gallium nitrate, ammonnium nitrade and distilled water was utilized as electrolyte. Platinum and p-Si were used as anode and cathode, respectively. After the deposition process of GaxOyNz/p-Si structure, temperature dependent Current-Voltage (I-V) measurements were performed and characterized between 20 °C and 100 °C in 10 °C steps to analyses of two dimensional density of interface states of the device. Characteristics show that GaxOyNz/p-Si device structure exhibits rectification behavior. [ABSTRACT FROM AUTHOR]

Ga2O3 has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of Ga2O3-based gas sensors. We begin with a brief introduction of the polymorphs and basic electric properties of Ga2O3. Next, we provide an overview of the typical preparation methods for the fabrication of Ga2O3-sensing material developed so far. Then, we will concentrate our discussion on the state-of-the-art Ga2O3-based gas sensor devices and put an emphasis on seven sophisticated strategies to improve their gas-sensing performance in terms of material engineering and device optimization. Finally, we give some concluding remarks and put forward some suggestions, including (i) construction of hybrid structures with two-dimensional materials and organic polymers, (ii) combination with density functional theoretical calculations and machine learning, and (iii) development of optical sensors using the characteristic optical spectra for the future development of novel Ga2O3-based gas sensors. [ABSTRACT FROM AUTHOR]

In inverted perovskite solar cells (PSCs), metal oxides become kind of promising hole transport layers for their facile synthesis and low cost. For conventional hole transport materials, the valence band match between metal oxides and perovskite layers is usually necessary for the hole extraction process. Ga2O3 is an emerging semiconductor material with ultrawide bandgap, but a significant energy level mismatch exists at Ga2O3/perovskite interfaces. In this work, Cu‐doped Ga2O3 (Ga2O3:Cu) nanocrystals are synthesized by the hydrothermal method and used as the hole transport material of inverted PSCs for the first time. It is found that Cu dopants can substantially improve the performance of Ga2O3 layers, and the efficiency of PSCs is increased from 7.6% to 19.5%. This improvement can be attributed to the additional hole transport channels from impurity levels of Cu dopants, which exactly match with the valence band of perovskite layers. As a consequence, Ga2O3:Cu layers can effectively extract holes and inhibit the recombination in perovskite layers. This work also provides an alternative route for the design of hole transport materials. [ABSTRACT FROM AUTHOR]

Gallium Oxide (Ga2O3) and Sapphire have been a preferred choice of substrates for fabricating $\beta $ -Ga2O3 Schottky barrier diodes (SBDs). However, Si (100) substrate with low cost and relatively high thermal conductivity has been explored as a platform in this work for the growth of $\beta $ -Ga2O3 using the pulsed laser deposition (PLD) technique. X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) results confirm the good crystalline quality and uniformity of the Ga2O3 film, respectively. The roughness (RMS) of 1.44 nm of the film surface is confirmed by the atomic force microscope (AFM) technique. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics are employed for investigating the electrical and interface trap properties of the SBDs. The Schottky barrier height measured at room temperature from I-V and C-V characteristics are 0.78 eV and 1.17 eV, respectively and the ideality factor turns out to be 1.95. The charge transport mechanism of SBD has been investigated using the log-log plot of I-V characteristics. The Schottky metal (Au)/ $\beta $ -Ga2O3 interface trap density ($D_{it}$) is obtained on the order of $\sim 10^{9}$ cm−2 eV−1 using the conventional conductance method. In the energy range of ${\text{E}}_{c}$ -0.27 eV to ${\text{E}}_{c}$ -1.57 eV, the density of interface states changes from $3.72\times 10^{9}$ eV−1cm−2 to $3.10\times 10^{9}$ eV−1cm−2, respectively. The maximum value of $D_{it}$ is found to be $4.38\times 10^{9}$ eV−1cm−2 at ${\text{E}}_{c}$ -0.68 eV. The value of $D_{it}$ can be further reduced for potential and reliable integration of $\beta $ -Ga2O3 with Si electronics. [ABSTRACT FROM AUTHOR]

Ga2O3 is one of the most suitable semiconductor materials for performing deep UV photoelectric detection. In this work, a self-powered deep UV photodetector based on a Ga2O3/BFO heterojunction is fabricated via solution spin-coating and metal-organic chemical vapor deposition (MOCVD) methods. Without biasing driven, the device achieves an extreme low dark current (${I}_{dark}$) of 8.38 fA, a photo-to-dark current ratio (PDCR) of $1.66\times10$ 5, a high specific detectivity (${D} \ast $) of $6.1\times 10^{12}$ Jones and an open-circuit voltage (${V}_{\textit {oc}}$) of 0.55 V responding to deep UV irradiation (254 nm in this work). Through analyzing the band diagram of the heterojunction, the intrinsic physical characteristics of the photodetector are discussed. Results show that the photodetector has excellent deep UV signal detecting ability, indicating that Ga2O3/BFO heterojunction is a potential candidate for performing self-powered deep UV photodetection. [ABSTRACT FROM AUTHOR]

In the present work, gallium oxide nanoparticles (nGa2O3) are synthesized via the thermal microwave combustion method, while nanocomposites of polyvinyl alcohol (PVA) polymer with various concentrations (0, 1, 2, 3, 4, and 5 wt%) of nGa2O3 are prepared by the casting technique. The structural characterization of nGa2O3, PVA, and films of PVA-Ga2O3 nanocomposites are studied using X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), and Fourier-transform infrared (FTIR) spectroscopy. The HRTEM and XRD examinations showed that the prepared nGa2O3 has an average crystallite size of ~ 5.6 nm and particle size of ~ 0.9 µm. The FTIR analysis reveals the occurrence of some interactions between nGa2O3 and the functional groups of the PVA structure. On another side, the refractive index, absorption coefficient, and optical bandgap (Eg) were determined using the Wemple-DiDomenico single oscillator model. It was shown that Eg slightly reduced from 3.61 to 3.55 eV with increasing the Ga2O3 content to 3 wt%, while raised again up to 3.58 eV for 5 wt% Ga2O3. Other optical characteristics such as the optical density, extinction coefficient, optical susceptibility, thermal emissivity, optical sheet resistance for the PVA−Ga2O3 nanocomposites are investigated. The linear and nonlinear optical parameters together with their dependencies on the doping ratio reveals the qualification of PVA−Ga2O3 nanocomposites for nonlinear optical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new system for in situ UV–vis measurement under reaction conditions is established. • Change of Ag states on Ga 2 O 3 is monitored in photocatalytic CO 2 reduction with H 2 O. • Light irradiation reduces Ag oxides initially deposited on Ga 2 O 3 to be Ag clusters. • Water enhances the reduction and assists aggregation of the nano-sized Ag particles. • CO 2 is adsorbed both on Ag oxide and Ag to retard their reduction and aggregation. Ag loaded Ga 2 O 3 photocatalysts are well known to be highly active for the CO 2 reduction with water to CO. However, Ag changes its chemical state during the reaction, resulting in the decrease of its photocatalytic activity. To examine the chemical state change during the photocatalytic CO 2 reduction, we have attempted a real time observation of the change in the chemical and physical states of Ag co-catalyst loaded on Ga 2 O 3 by monitoring UV–vis reflectance spectra under the atmosphere simulating the photocatalytic CO 2 reduction. In UV–vis spectra, two characteristic absorptions appeared at around 450 nm and 600 nm corresponding to resonance absorptions of localized surface plasmon (LSPR) of Ag nanoparticles (Ag-NPs) and Ag in metallic state. The LSPR absorption appeared as light irradiation started and grew with the time. It was revealed that Ag on Ga 2 O 3 was initially in the oxidized state and reduced by the light irradiation to be Ag-NPs. Further light irradiation enlarged the size of Ag-NPs to be the metallic state especially under atmosphere with water. Under CO 2 atmosphere, Ag-NPs remained small after further light irradiation. These results suggest that Ag initially loaded on Ga 2 O 3 in the oxidized state was reduced to be dissolved as Ag+ in water and precipitated as Ag-NPs. Then, some of Ag-NPs aggregated to be larger Ag particles or in the metallic state. Such reduction process depends on gas species of the system, i.e. water promoted the formation of Ag-NPs while CO 2 suppressed the formation Ag-NPs. [ABSTRACT FROM AUTHOR]

A new device structure, which includes a Ga2O3 current blocking layer (CBL) and a Ga2O3 surface passivation layer (SPL), is used to fabricate a GaN-based light-emitting diode (LED). Due to the inherent properties of Ga2O3 material, the current spreading phenomenon can be effectively improved and the surface leakage current and Fresnel reflection can be remarkably reduced. The appropriate thicknesses of the Ga2O3 CBL and SPL, according to the results from series experiments, are 10 and 50 nm, respectively. In an experiment, under an injection current density of 100 A/cm2, the studied LED device with a 10 nm-thick Ga2O3 CBL and a 50 nm-thick Ga2O3 SPL shows enhancements of 76.8%, 60.7%, 76.8%, and 56.2% in light output power (LOP), luminous efficacy, external quantum efficiency (EQE), and wall-plug efficiency, respectively, in comparison to a conventional LED without the designed structure. In addition, the studied LED exhibits obvious improvement in far-field radiation pattern compared to the conventional LED device. Thus, the studied structure, which includes an appropriate Ga2O3 CBL and SPL, offers a promising route to fabricate high-performance GaN-based LEDs. [ABSTRACT FROM AUTHOR]

β-Ga2O3 is a candidate for high-efficiency power electronics and ultraviolet C (UVC) detectors capable of operating in harsh environments. However, electrical contacts that maintain their performance at high temperatures are likely to be important due to the material’s low thermal conductivity. In this study, we report on a dramatic improvement in the rectifying performance of Pd Schottky contacts (SCs) on (201) and (010) β-Ga2O3 at high temperatures in air. This effect involves a large thermally activated increase in the image-force-corrected barrier height (ΦB,IF) from 1.40 eV at room temperature (RT) to 1.75–2.20 eV, with most of the transition occurring between 250 °C and 450 °C. This improvement is due to the oxidation of the Pd SC layer that creates higher barrier height PdO regions that dominate the high-temperature current transport. In the most oxidized Pd SCs, ΦB,IF increased to 2.20 eV at 500 °C with leakage currents of ~ 1 × 10−6 Acm−2 (−3 V) and rectification ratios (±3 V) of ~ 107, at 500 °C, similar to the best results for diamond and SiC SCs. Interestingly, very good agreement between the temperature dependence of the built-in voltage of the thermally oxidized Pd SCs and the optical bandgap of β-Ga2O3 (approximately −1.3 meV/°C in both cases) was observed between RT and 500 °C. [ABSTRACT FROM AUTHOR]

With projected performance advantages over silicon and incumbent wide-bandgap compound semiconductors, gallium oxide (Ga2O3) has garnered worldwide attention as an ultrawide-bandgap semiconductor material suitable for high-voltage, high-temperature, and radiation-hard electronics. Thanks to recent breakthroughs in crystal growth and device processing technologies, the research and development of vertically oriented Ga2O3 power transistors has made rapid strides. In this article, we review the important engineering achievements and performance milestones of the two major types of vertical Ga2O3 transistors—current aperture vertical metal–oxide–semiconductor field-effect transistors (MOSFETs) and vertical fin-channel MOSFETs. Challenges underlying the unique processing approaches to these devices and their implications on device reliability are also discussed. [ABSTRACT FROM AUTHOR]

We present a detailed investigation of the trapping and detrapping mechanisms that take place in the gate region of β-Ga2O3 vertical finFETs and describe the related processes. This analysis is based on combined pulsed characterization, transient measurements, and tests carried out under monochromatic light, with photon energies between 1.5 and 5 eV. The original results presented in this article demonstrate that: (i) when submitted to positive gate stress with VGS > 3 V, the devices show a significant threshold voltage variation; (ii) this effect is not recoverable in 10 000 s in rest condition (zero bias, dark condition). (iii) VTH can quickly recover its initial value when the device is illuminated with UV-C light at 280 nm. (iv) Stress-recovery experiments carried out at different photon energies allowed us to estimate the threshold energy for the release of carriers from the Al2O3/Ga2O3 interface, and for the injection of electrons from metal to the Al2O3 insulator (conduction band discontinuity at the metal/Al2O3 interface). [ABSTRACT FROM AUTHOR]

Regardless of much curiosity in the synthesis and diversifying properties of the polymorphs of gallium oxide, they are still unrevealed due to their nanoscale size and structural disorders. In this study, convincing methods have been applied to achieve various phases of gallium oxide (i.e., GaOOH, α-Ga2O3, β-Ga2O3, γ-Ga2O3, δ-Ga2O3, and ε-Ga2O3). X-ray diffraction (XRD) along with Rietveld refinement has been employed to investigate the structural parameters of barely reported phases. Transmission electron microscopy (TEM) images reveal the impact of the protocols of chemical synthesis on the morphology/size of the polymorphs of gallium oxide. Mechanistic discussion on the formation of nano-rod morphology in some of the phases (GaOOH and α-Ga2O3) and nano-particle morphology in other (β-Ga2O3, γ-Ga2O3, δ-Ga2O3 and ε-Ga2O3) phases is also provided by considering the experimental parameters. The existence of Ga3+ ions and their local hybridization with the oxygen is investigated using the X-ray absorption spectroscopy (XAS) at Ga K-edge and conveyed the phase dependence on the hybridization of frontier orbitals. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga 2 O 3) has drawn great attention due to its potential application as a transparent conducting film. However, unavoidable oxygen vacancy (V O) induces the impurity level in the band gap, weakening the transparency of Ga 2 O 3. On the other hand, the V O provides extra electron carriers, facilitating conductivity. Thus, coordinating the relation between the transparency and conductivity becomes rather urgent. Here, we propose that a co-dopant of aluminum (Al) and indium (In), together with oxygen vacancy (Al Ga -In Ga -V O), is a control method to eliminate the opaqueness and to simultaneously take advantage of the extra electron carriers resulting from the V O. First-principles electronic structure calculations reveal that Al Ga with V O (Al Ga -V O) does not eliminate the undesirable absorption of V O , whereas In Ga -V O does. The defect formation energy of In Ga -V O is higher than that of Al Ga -V O. Intriguingly, Al Ga -In Ga -V O not only reduces the defect formation energy but also maintains the transparency of perfect Ga 2 O 3. The strong hybridization between In 4d and O 2p induces the downshift of the impurity level, enhancing the optical bandgap. Our work indicates that doping equivalent elements might provide an effective way to achieve high transparent β -Ga 2 O 3. Image 1 • High transparent Ga 2 O 3 is achieved via co-dopant of Al and In together with V O. • Enhancing the content of Al further increases the solubility of In. • Doping equivalent elements modulates the impurity level of V O. • Our results might provide a theoretical basis for the experimental study. [ABSTRACT FROM AUTHOR]

In this work, the thermal synthesis and characterization of gallium oxide and indium oxide nanowires using vapour-liquid-solid mechanism at atmospheric pressure were described. Au nanoislands formed by the solid-state dewetting process of various thickness metal layer were applied as growth catalyst of nanowires while high-purity metal reactants (In, Ga) were applied as AIII precursors. The catalytic layer thickness influence on the morphology of investigated nanostructures was studied. Material composition and structural properties were used for crystallographic quality of AIII-oxide nanowires examination. [ABSTRACT FROM AUTHOR]

Ga2O3 has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga2O3 power devices stimulated by early demonstrations of high-voltage Ga2O3 field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga2O3 FETs — which have predominantly been lateral devices — for power switching and radiation-hard electronics. The development of vertical Ga2O3 transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed. [ABSTRACT FROM AUTHOR]

Depletion-mode vertical Ga2O3 metal-oxide-semiconductor field-effect transistors featuring a current aperture were developed on a halide vapor phase epitaxial drift layer grown on a bulk $\beta $ -Ga2O3 (001) substrate. Three ion implantation steps were employed to fabricate the ${n}^{++}$ source regions, lateral ${n}$ channel, and ${p}$ current blocking layers, where Si and N were selected as the donor and deep acceptor dopant species, respectively. The transistors delivered a drain current density of 0.42 kA/cm2, a specific on-resistance of 31.5 $\text{m}\Omega \cdot \text {cm}^{2}$ , and an output current on/off ratio of over 108. High-voltage performance of the present devices was hampered by a large gate oxide field in the off-state causing high gate leakage, a limitation that can be readily overcome through optimized doping schemes and an improved gate dielectric. The demonstration of a planar-gate vertical Ga2O3 transistor based on a highly manufacturable all-ion-implanted process greatly enhances the prospects for Ga2O3-based power electronics. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga 2 O 3) with an ultrawide bandgap, is a promising and inherent material for solar-blind photodetectors (SBPDs). However, it remains a challenge to achieve a photodetector with large responsivity and fast response speed owing to the presence of intrinsic oxygen vacancies (V O) in the Ga 2 O 3 films. Here, the annealing and doping engineering is proposed to break the compromise between the responsivity and response speed, based on the low-cost method for annealing nitrogen-doped Ga 2 O 3 films with various concentrations of V O in Ar, O 2 , and N 2 atmospheres. The mechanism of regulating V O in the nitrogen-doped Ga 2 O 3 films under various annealing atmospheres has been clarified first. The influence of concentrations of V O in pristine films and annealing atmospheres on the photoelectric properties of annealed films was analyzed systematically. The nitrogen-doping, recrystallization, and the appropriate concentration of V O in pristine Ga 2 O 3 films are favorable factors for optimizing the properties of the post-annealing Ga 2 O 3 films. The photodetectors based on annealing and doping engineering exhibit impressive characteristics with high photo-to-dark current ratios (PDCRs) of 2.6 × 107, large rejection ratio of R 254 /R 365 = 1.0 × 106, especially the faster response speed of 0.359/0.110 s, 9.8 times higher R 254 , and 6.34 × 102 times lower I dark than pristine films. The regulation of V O via doping and annealing methods can provide an effective strategy for low-cost high-performance Ga 2 O 3 -based SBPDs. • A method combining annealing and elemental doping enhances responsivity and alleviates PPC effect. • Explaining the influence of V O concentration on properties of pristine Ga 2 O 3 films and post-annealed one. • The mechanisms for regulating V O in different annealed atmospheres were clarified. • The N-doping and appropriate concentration of V O could optimize the properties of the post-annealing Ga 2 O 3 films. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Work function modification of unintentionally doped β-Ga 2 O 3 thin films is reported. • Both oxygen rich and oxygen deficient growth conditions were responsible for FLP which resulted in high work function. • No FLP was observed for thin films grown at intermediate oxygen pressure, even though the stoichiometry was not achieved. • Relative tuning of A g 3 and A g 6 Raman phonon modes with change in density of tail states of VBM has been clearly observed. • The mechanism to control FLP in UID β-Ga 2 O 3 has been proposed. Abstract Effect of point defects such as vacancies and interstitials on the work function of β-Ga 2 O 3 thin films grown by pulsed laser deposition was investigated. Relative change in A g 3 and A g 6 Raman phonon modes indicated formation of oxygen and gallium vacancy defects. The surface potential mapping of Ga 2 O 3 thin films was performed by Kelvin probe force microscopy. Analytical calculations showed variation in work function with oxygen pressure. The work function values at extreme growth pressure conditions were found to be very high. Hence, Fermi level was pinned at the mid-gap energy in both oxygen-deficient condition and oxygen-rich conditions which is attributed to oxygen and gallium vacancy defects. This mechanism of controlling Fermi level pinning in β-Ga 2 O 3 paves the way to fabricate high performance electronic devices. [ABSTRACT FROM AUTHOR]

We calculate analytically, the epitaxial in-plane and out-of-plane strains for pseudomorphic growth of monoclinic heterostructures for various substrate orientations, namely the (010) plane and all ( [ABSTRACT FROM AUTHOR]

Patterned gallium oxide (Ga2O3) using one-step patterning followed by oxygen plasma treatment on a p-GaN layer can function as both current-blocking and optical-scattering regions for uniform current spreading and improved light-extraction efficiencies. The results showed that the optical output power of the LED with patterned Ga2O3 increased by 16.8% at 60 mA compared to that of conventional LEDs. Numerical studies on light tracing and emission pattern, and external quantum efficiency evaluation support the improvement of both uniform current spreading and light-extraction efficiencies by patterned Ga2O3. [ABSTRACT FROM AUTHOR]

We have used X-ray pole figure analysis to study crystal orientations of β-Ga2O3 thin films deposited on (113) n-plane sapphire substrates by gallium evaporation in oxygen plasma. The films were strongly (−201)-oriented. However, the (−201) plane of β-Ga2O3 on the (113) n-plane sapphire was inclined along the (110) a-plane. Crystals of (−201)-oriented β-Ga2O3 exhibit a threefold symmetry in which the β-Ga2O3 crystal is rotated by increments of 120° from the direction of the c-axis on the a-plane of sapphire. The crystal orientation of β-Ga2O3 was explained by comparing oxygen atom arrangements on the β-Ga2O3 plane in three different configurations and on the (113) n-plane sapphire substrates. [ABSTRACT FROM AUTHOR]

A new heteroleptic gallium (III) alkyl amidinate [monoacetamidinatodiethylgallium(III), compound 1] was found to undergo self-seeding pulsed chemical vapor deposition (p-CVD) to gallium metal above temperatures of 450 °C. Below this temperature, the mono-layer formed on the surface of silica and alumina is unreactive to itself and H2O and O2 co-reactants. With no co-reactant above 450 °C gallium metal spheres (150-500 nm) was formed in a p-CVD experiment. With the addition of short H2O pulses produced interesting morphologies and gallium metal/gallium oxide structures resembling 'ice cream cones' of varying sizes (<150-500 nm). The addition of O2 produced micron long nanowires <250 nm in width and a mat of nanoparticles on both silicon and alumina. Scanning electron micrograph of pulsed chemical vapor deposition of 1 with H2O as a co-reactant at 500 °C. [ABSTRACT FROM AUTHOR]

We have used X-ray pole figure analyses to study crystal orientations of β-Ga2O3 thin films formed on (100) m-plane or (102) r-plane sapphire substrates prepared by gallium evaporation in oxygen plasma. The (−201) plane of β-Ga2O3 on the (100) m-plane was inclined to be along two (110) a-planes. Crystals of (−201)-oriented β-Ga2O3 exhibit six-fold symmetry in which a β-Ga2O3 crystal is rotated every 60° from [001] for each a-plane. In all, twelve kinds of β-Ga2O3 crystals formed on m-plane sapphire substrate. Similarly, the (−201) plane of β-Ga2O3 on the (102) r-plane was inclined to be along to two (113) n-plane. Crystals of (−201)-oriented β-Ga2O3 exhibit three-fold symmetry with a β-Ga2O3 crystal rotated every 120° from the opposite direction of projection of the c-axis of each n-plane. In all, six kinds of β-Ga2O3 crystals formed on the r-plane sapphire substrate. These observations can be explained by comparing oxygen atomic arrangements on the β-Ga2O3 (−201) plane with those on the sapphire (110) a-plane and (113) n-plane. [ABSTRACT FROM AUTHOR]

Effect Ga2O3 addition on the densification and properties of Y2O3-doped AlN ceramics was investigated under the constraint of total sintering additives (Y2O3 and Ga2O3) of 4.5 wt%. Ga was detected in the AlN grain as well as the grain boundary phases. YAlO3 and Y4Al2O9 were observed as the secondary crystalline phases in all of the investigated compositions. As the substitution of Ga2O3 for Y2O3 increased, the quantity of the Y4Al2O9 phase decreased while that of YAlO3 was more or less similar. Neither additional secondary phases was identified, nor was the sinterability inhibited by the Ga2O3 addition; the linear shrinkage and apparent density were above 20 percent and 3.34-3.37 g/cm³, respectively. However, the optical reflectance and the elastic modulus generally decreased whereas the Poisson ratio increased significantly. The dielectric constant and the loss tangent of 4.0Y2O3- 0.5Ga2O3-95.5Y2O3 at the resonant frequency of 8.22 GHz were 8.63 and 0.003, respectively. [ABSTRACT FROM AUTHOR]

We investigated the use of transparent conductive oxide for near-ultraviolet light-emitting diodes based on co-sputtered gallium oxide (Ga2O3) and indium tin oxide (ITO). The electrical and optical properties of Ga2O3/ITO (IGTO) were observed to improve through hydrogen annealing, which resulted in a sheet resistance of 164 Ω/□ and an optical transmittance of 94% at increased carrier concentration and crystallization of the co-sputtered film through hydrogen annealing. Moreover, ohmic-like contacts were formed on the p-GaN substrate with a specific contact resistance of 3.9 × 10−1 Ω cm2. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) is a strong contender for power electronic devices. The material possesses excellent properties such as a large bandgap of 4.7-4.9 eV for a high breakdown field of 8 MV cm−1. Low cost, high volume production of large single-crystal β-Ga2O3 substrates can be realized by melt-growth methods commonly adopted in the industry. High-quality n-type Ga2O3 epitaxial thin films with controllable carrier densities were obtained by ozone molecular beam epitaxy (MBE). We fabricated Ga2O3 metal-semiconductor field-effect transistors (MESFETs) and Schottky barrier diodes (SBDs) from single-crystal Ga2O3 substrates and MBE-grown epitaxial wafers. The MESFETs delivered excellent device performance including an off-state breakdown voltage ( Vbr) of over 250 V, a low leakage current of only few μA mm−1, and a high drain current on/off ratio of about four orders of magnitude. The SBDs also showed good characteristics such as near-unity ideality factors and high reverse Vbr. These results indicate that Ga2O3 can potentially meet or even exceed the performance of Si and typical widegap semiconductors such as SiC or GaN for ultrahigh-voltage power switching applications. [ABSTRACT FROM AUTHOR]

The authors report the conversion of AlGaN epitaxial layer into (Alx\rm Ga1-{\rm x)}2{\rm O}3 thin film by furnace oxidation at high temperature in oxygen containing ambient. A vacuum-ultraviolet (Alx\rm Ga1-{\rm x)}2{\rm O}3 photodetector (PD) was also fabricated. It was found that external quantum efficiency of the fabricated PD measured at 220 nm was 30%. It was found that the fabricated PD exhibits extremely large deep-UV-to-visible rejection ratio. [ABSTRACT FROM PUBLISHER]

Abstract: Solvothermal oxidation of gallium metal in various organic solvents at 300°C under the autogenous vapor pressure of the solvents was examined. The reaction of gallium metal in 1-butanol or 2-methoxy-ethanol at 300°C did not proceed and unreacted gallium metal was recovered even with prolonged reaction time. On the other hand, gallium metal reacted in aminoalcohols such as 2-aminoethanol, 2-methylaminoethanol, 2,2′-iminodiethanol and 2,2′,2″-nitrilotriethanol yielding γ-Ga2O3. The product obtained by this reaction has a relatively large crystallite size as compared with γ-Ga2O3 prepared by the conventional method. [Copyright &y& Elsevier]

Abstract: We report on several methods for synthesizing the ultra-fast scintillator ZnO(Ga), and measurements of the resulting products. This material has characteristics that make it an excellent alpha detector for tagging the time and direction of individual neutrons produced by t–d and d–d neutron generators (associated particle imaging). The intensity and decay time are strongly dependent on the method used for dopant incorporation. We compare samples made by diffusion of Ga metal to samples made by solid-state reaction between ZnO and Ga2O3 followed by reduction in hydrogen. The latter is much more successful and has a pure, strong near-band-edge fluorescence and an ultra-fast decay time of the X-ray-excited luminescence. The luminescence increases dramatically as the temperature is reduced to 10K. We also present results of an alternate low-temperature synthesis that produces luminescent particles with a more uniform size distribution. We examine possible mechanisms for the bright near-band-edge scintillation and favor the explanation that it is due to the recombination of Ga3+ donor electrons with ionization holes trapped on H+ ion acceptors. [Copyright &y& Elsevier]

Interest in the synthesis and fabrication of gallium oxide (Ga2O3) nanostructures as wide bandgap semiconductor-based ultraviolet (UV) photodetectors has recently increased due to their importance in cases of deep-UV photodetectors operating in high power/temperature conditions. Due to their unique properties, i.e., higher surface-to-volume ratio and quantum effects, these nanostructures can significantly enhance the sensitivity of detection. In this work, two Ga2O3 nanostructured films with different nanowire densities and sizes obtained by thermal oxidation of Ga on quartz, in the presence and absence of Ag catalyst, were investigated. The electrical properties influenced by the density of Ga2O3 nanowires (NWs) were analyzed to define the configuration of UV detection. The electrical measurements were performed on two different electric contacts and were located at distances of 1 and 3 mm. Factors affecting the detection performance of Ga2O3 NWs film, such as the distance between metal contacts (1 and 3 mm apart), voltages (5–20 V) and transient photocurrents were discussed in relation to the composition and nanostructure of the Ga2O3 NWs film. [ABSTRACT FROM AUTHOR]

Abstract: Novel MCM-41 modified catalytic materials were synthesized by impregnation of MCM-41 with niobium and gallium salts. A number of techniques, including nitrogen adsorption, X-ray diffraction, FT-IR and Raman spectroscopies, have been used to characterize a series of gallium and niobium-containing composite materials, aimed especially at the rationalization of the nature of oxides species formed. Generally, the presence of highly dispersed NbO x and GaO x moieties in the mesoporous materials could be deduced from this approach. It has been demonstrated that incorporation of gallium and niobium into the MCM-41 type silica matrix leads to formation of active and selective catalysts for the oxidation of hydrocarbons. [Copyright &y& Elsevier]

By using a He-Cd laser in a chemical solution of H3PO4 with a pH value of 3.5, Ga oxide films were directly grown on n-type GaN. From the energy-dispersive spectrometer (EDS) measurement and x-ray diffraction (XRD) measurement, the grown Ga oxide film was identified as (104) α-Ga2O3 structure. A small amount of phosphors existed and bonded with oxygen on the grown films. The as-grown films were amorphous. From the XRD analysis, it is evident that annealing of the α-Ga2O3 films led to a change in the microstructure from an amorphous to a polycrystalline phase. In addition, the as-grown low-density films gradually became dense films during the annealing process. Furthermore, the surface roughness of the annealed films also gradually decreased. Hexagonal pinholes on the grown films were observed. The density of the hexagonal pinholes was similar to the defect density of the n-type GaN. From the cross-sectional transmission electron microscopy (TEM) micrographs, it is evident that the hexagonal pinholes originated from defects in the n-type GaN. [ABSTRACT FROM AUTHOR]

We have prepared the gallium oxide (Ga2O3) thin films on sapphire substrates by the metal organic chemical vapor deposition (MOCVD) technique. We have compared the two films with and without the thermal annealing by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and the photoluminescence (PL) spectra. Postdeposition annealing of amorphous Ga2O3 films was found to increase the degree of crystallization and the surface roughness. The PL emission intensities of bands in the blue–green and the ultraviolet regions increased by the thermal annealing. [Copyright &y& Elsevier]

[Display omitted] • Ga 2 O 3 nitridation with NH 3 to GaN occurs via amorphous gallium oxynitrides intermediates. • NH 3 adsorption was barrier less in which N is attracted towards gallium (Ga–N). • Two limiting steps: (1) N–H dissociation from the first NH 2 * to NH* and (2) last H 2 O release. • Pore diffusion influence the GaN formation at high temperatures and high conversions. TG experiments and DFT calculations were used to investigate the mechanism of gallium oxide nitridation to gallium nitride. The overall conversion of the gas-solid reaction can be best described by a modified integrated model that accounts for diffusion influence at high temperatures and conversions. For that model, an apparent activation energy of 154 kJ mol−1 and a reaction order for Ga 2 O 3 of n = 0.36 were estimated. NH 3 favorably adsorbed on Ga 2 O 3 without any energy barrier in which the nitrogen is attracted towards gallium (Ga–N). The Ga 2 O 3 surface was nitridated to GaN via adsorbed NH 2 *, NH* and H* intermediates, obtained through NH 3 * dissociation, increasingly stabilized by the surface, preventing their early desorption, and testifying of the positive nitrogen (N) atom insertion into the crystal. The N–H bond became harder to break, increasing the dissociation reaction and activation energies. The first NH 2 * dissociation to NH* was a limiting step, with a high activation energy of 2.81 eV. The second limiting step was the formation of the third H 2 O molecule with an activation energy of 3.07 eV. According to the observations, the first layer of GaN was organized towards the wurtzite crystal structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Post-deposition annealing of Ga 2 O 3 was done in nitrogen/oxygen/nitrogen ambient. • Dual properties of polycrystalline Ga 2 O 3 films were formed. • The films obtained at 400 and 600 °C demonstrated semiconducting property. • The films obtained at 800 and 1000 °C were insulating. • Oxygen vacancies and nitrogen incorporation led to high leakage current. Polycrystalline Ga 2 O 3 films were obtained after post-deposition annealing of as-deposited Ga 2 O 3 films via radio frequency magnetron sputtering at different temperatures (400, 600, 800, and 1000 °C) in nitrogen/oxygen/nitrogen ambient. The Ga 2 O 3 films obtained at lower temperatures (400 and 600 °C) demonstrated semiconducting property while the films obtained at higher temperatures (800 and 1000 °C) demonstrated insulating property based upon the leakage current density-voltage characteristics. The semiconducting properties were originated from the presence of oxygen vacancies as well as nitrogen incorporation as the scattering centre in the films, which could serve as the conducting path of electrons, encouraging a higher leakage current. The acquisition of a smaller direct and indirect band gap by these films further supported the fact that electrons would overcome the potential barrier easier. On the other hands, the presence of oxygen vacancies and nitrogen incorporation as well as preferred orientation of film growth accompanied with dislocation affected the leakage current density-voltage characteristics. Detailed investigation in the aspects of structural, morphological, optical, and electrical characteristics of the films was demonstrated. [ABSTRACT FROM AUTHOR]

A fast-response colorimetric ultraviolet-C (UVC) sensor was demonstrated using a gallium oxide (Ga2O3) photocatalyst with small amounts of triethanolamine (TEOA) in methylene blue (MB) solutions and a conventional RGB photodetector. The color of the MB solution changed upon UVC exposure, which was observed using an in situ RGB photodetector. Thereby, the UVC exposure was numerically quantified as an MB reduction rate with the R value of the photodetector, which was linearly correlated with the measured spectral absorbance using a UV-Vis spectrophotometer. Small amount of TEOA in the MB solution served as a hole scavenger, which resulted in fast MB color changes due to the enhanced charge separation. However, excessive TEOA over 5 wt.% started to block the catalytical active site on the surface of Ga2O3, prohibiting the chemical reaction between the MB molecules and catalytic sites. The proposed colorimetric UVC sensor could monitor the detrimental UVC radiation with high responsivity at a low cost. [ABSTRACT FROM AUTHOR]

Our laboratory has previously revealed the use of metal-semiconductor-metal (MSM) varactors against malicious pulses, as well as completed the related verification and measurements of such a circuit. To improve the reliability of this protection module further, in this study, we deposited a gallium oxide (Ga2O3) thin film in between the Schottky contact electrode to manufacture a metal-oxide-semiconductor-oxide-metal (MOSOM) varactor. However, the thin-film quality and heterojunction interfaces will affect these fabricated varactors in various ways, such as the asymmetry threshold voltage to the variable capacitance characteristics. This study aims to address the issues associated with the inserted oxide thin film, as well as to determine how improvements could be obtained by using an oxygen furnace annealing process. As a result, the breakdown voltage of the MOSOM varactor was further promoted and a more robust anti-surge module was thus realized. [ABSTRACT FROM AUTHOR]

Microstructures of gallium oxide with diverse morphologies are synthesized using vapor phase transport route. Structural and micro structural investigations using XRD, SEM and micro Raman technique confirm formation of single phase β-Ga 2 O 3. Morphology and structural quality of the crystal growth is observed to improve with respect to growth temperature. Based on observations suitable growth mechanism is proposed to explain diverse morphologies governed by the growth temperatures. From Field Emission (FE) investigations, the structural defects associated with the crystal growth are claimed to affect the FE properties. Adequate field emission followed by steady current recorded over a long period of time for micron sized sheets of β-Ga 2 O 3 (specimen synthesized at 1000 °C) looks favorable for various FE applications. The results are very promising looking at the possibilities to fabricate uniform, homogeneous layers of the active material, retaining excellent FE properties observed during various nano-forms of β-Ga 2 O 3 otherwise. • Growth of gallium oxide microstructures using vapor phase transport route. • The β-Ga 2 O 3 morphological changes are reported as a function of growth temperature. • Deformation and stress produced in crystals is observed to be a function of growth temperature. • Based on observations suitable growth mechanism is proposed herewith. • Adequate field emission followed by steady current is observed from micron sized sheets of β-Ga 2 O 3. [ABSTRACT FROM AUTHOR]

• The effect of gallium content on PCH support for SCR activity was proposed. • 90 % NO conversion by C 3 H 6 over 24 wt% Ga-PCH catalyst at 350 °C. • Well dispersion of Ga in PCH support is achieved via high NO conversion. • Gallium loading increases lewis acid site and decreases Bronsted acidic site. • Strong stability of Ga-PCH catalyst for NO and better resistance to H 2 O and SO 2. The porous clay heterostructures (PCHs) were used as a carrier for gallium oxide-based catalyst to convert the nitrogen oxide (NO) to N 2 with C 3 H 6. The ICP, N 2 physisorption, XRD, SEM, XPS, UV-vis and Py-FTIR tests were applied to study the physicochemical properties and the selective catalytic reduction of NO was evaluated in a fixed-bed reactor by C 3 H 6. The catalysts with different Ga loading, i.e., 7, 13, 24 and 32 wt% were tested and the best catalytic activity was achieved at 24 wt% Ga-PCH, which exhibits 90% NO x conversion at 350 °C, strong thermal stability and better resistance to H 2 O and SO 2. Further, the NO x conversion test demonstrated that adding a small concentration of gallium oxide on porous clay support improves the catalytic efficiency by increasing the acidic concentration and amorphous formation that is beneficial for the conversion of nitrogen oxide (NO) at low temperatures. Meanwhile, the increase of gallium content might be a reason for the agglomeration of Ga 2 O 3 molecules and blockage of Porous Clay Heterostructures (PCHs) support pores. [ABSTRACT FROM AUTHOR]

• Ga 2 O 3 photocatalysts are prepared by calcining Ga(NO 3) 3 ·8H 2 O at 673 1173 K in air. • The Ga 2 O 3 photocatalysts promote photocatalytic CO 2 reduction and H 2 O splitting. • CO 2 reduction and H 2 O splitting proceed independently. • H 2 production rate increases with Ga 2 O 3 surface area but CO production rate does not. • γ, β mixed phase Ga 2 O 3 shows the highest activity, even higher than Ag loaded ones. Ga 2 O 3 samples were synthesized by calcination of gallium nitrate powder at a given temperature ranging from 673 K to 1173 K (denoted as T-Ga 2 O 3 with T, calcination temperature). XRD and XAFS structural analyses revealed that samples calcined at temperatures below 673 K were consisted of defective ε phase, whereas those calcined above 773 K of β and γ phases, and β phase dominated above 923 K. All calcined Ga 2 O 3 samples promoted photocatalytic CO 2 reduction with water to produce CO, H 2 and O 2. As for the H 2 production by water splitting, the H 2 production rates were well correlated with the surface areas of calcined Ga 2 O 3 samples. It was also found that the water splitting and the CO 2 reduction proceeded fully independently. 823-Ga 2 O 3 showed the highest activity for the CO 2 reduction, suggesting that the coexistence of β and γ phases plays a key role on the photocatalytic CO 2 reduction. [ABSTRACT FROM AUTHOR]