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11 pages, 4413 KiB

Open AccessArticle

Structure and Chemical Composition of Ion-Synthesized Gallium Oxide Nanocrystals in Dielectric Matrices

by Dmitry S. Korolev, Ruslan N. Kriukov, Kristina S. Matyunina, Alena A. Nikolskaya, Alexey I. Belov, Alexey N. Mikhaylov, Artem A. Sushkov, Dmitry A. Pavlov and David I. Tetelbaum

Nanomaterials 2023, 13(10), 1658; https://doi.org/10.3390/nano13101658 - 17 May 2023

Cited by 1 | Viewed by 1210

Abstract

The ion-beam synthesis of Ga₂O₃ nanocrystals in dielectric matrices on silicon is a novel and promising way for creating nanomaterials based on gallium oxide. This research studies the regularities of changes, depending on the synthesis regimes used, in the chemical [...] Read more.

The ion-beam synthesis of Ga₂O₃ nanocrystals in dielectric matrices on silicon is a novel and promising way for creating nanomaterials based on gallium oxide. This research studies the regularities of changes, depending on the synthesis regimes used, in the chemical composition of ion-implanted SiO₂/Si and Al₂O₃/Si samples. It has been shown that the formation of Ga-O chemical bonds occurs even in the absence of thermal annealing. We also found the conditions of ion irradiation and annealing at which the content of oxidized gallium in the stochiometric state of Ga₂O₃ exceeds 90%. For this structure, the formation of Ga₂O₃ nanocrystalline inclusions was confirmed by transmission electron microscopy. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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13 pages, 3007 KiB

Open AccessArticle

The Influence of Process Parameters on the Microstructural Properties of Spray-Pyrolyzed β-Ga₂O₃

by Constance Schmidt, Axel Fechner, Oleksandr Selyshchev and Dietrich R. T. Zahn

Nanomaterials 2023, 13(9), 1455; https://doi.org/10.3390/nano13091455 - 25 Apr 2023

Cited by 1 | Viewed by 1361

Abstract

In this work, the deposition of β-Ga₂O₃ microstructures and thin films was performed with Ga(NO₃)₃ solutions by ultrasonic nebulization and spray coating as low-cost techniques. By changing the deposition parameters, the shape of β-Ga₂O₃ [...] Read more.

In this work, the deposition of β-Ga₂O₃ microstructures and thin films was performed with Ga(NO₃)₃ solutions by ultrasonic nebulization and spray coating as low-cost techniques. By changing the deposition parameters, the shape of β-Ga₂O₃ microstructures was controlled. Micro-spheres were obtained by ultrasonic nebulization. Micro-flakes and vortices were fabricated by spray coating aqueous concentrated and diluted precursor solutions, respectively. Roundish flakes were achieved from water–ethanol mixtures, which were rolled up into tubes by increasing the number of deposition cycles. Increasing the ethanol-to-water ratio allows continuous thin films at an optimal Ga(NO₃)₃ concentration of 0.15 M and a substrate temperature of 190 °C to be formed. The monoclinic β-Ga₂O₃ phase was achieved by thermal annealing at 1000 °C in an ambient atmosphere. Scanning electronic microscopy (SEM), X-ray diffraction (XRD), and UV-Raman spectroscopy were employed to characterize these microstructures. In the XRD study, in addition to the phase information, the residual stress values were determined using the sin²(ψ) method. Raman spectroscopy confirms that the β-Ga₂O₃ phase and relative shifts of the Raman modes of the different microstructures can partially be assigned to residual stress. The high-frequency Raman modes proved to be more sensitive to shifting and broadening than the low-frequency Raman modes. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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11 pages, 3328 KiB

Open AccessArticle

Temperature-Dependent and Time-Resolved Luminescence Characterization of γ-Ga₂O₃ Nanoparticles

by Marina García-Carrión, Julio Ramírez-Castellanos, Emilio Nogales and Bianchi Méndez

Nanomaterials 2023, 13(9), 1445; https://doi.org/10.3390/nano13091445 - 23 Apr 2023

Cited by 1 | Viewed by 1612

Abstract

The temperature-dependent luminescence properties of γ-Ga₂O₃ nanoparticles prepared by a precipitation method are investigated under steady-state and pulsed-light excitation. The main photoluminescence (PL) emission at room temperature consists of a single blue band centered around 2.76 eV, which hardly undergoes [...] Read more.

The temperature-dependent luminescence properties of γ-Ga₂O₃ nanoparticles prepared by a precipitation method are investigated under steady-state and pulsed-light excitation. The main photoluminescence (PL) emission at room temperature consists of a single blue band centered around 2.76 eV, which hardly undergoes a blueshift of 0.03 eV when temperature goes down to 4 K. The emission behaves with a positive thermal quenching following an Arrhenius-type curve. The data fitting yields two non-radiative levels affecting the emission band with activation energies of 7 meV and 40 meV. On the other hand, time-resolved PL measurements have also been taken and studied as a function of the temperature. The data analysis has resulted in two lifetimes: one of 3.4 ns and the other of 32 ns at room temperature, which undergo an increase up to 4.5 ns and 65 ns at T = 4 K, respectively. Based on both stationary and dynamic PL results, a model of radiative and non-radiative levels associated with the main emission bands of γ-Ga₂O₃ is suggested. Finally, by using PL excitation measurements, an estimation of the bandgap and its variation with temperature between 4 K and room temperature were obtained and assessed against O’Donnell–Chen’s law. With this variation it has been possible to calculate the average of the phonon energy, resulting in ⟨ħω⟩ = 10 ± 1 meV. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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22 pages, 8730 KiB

Open AccessArticle

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga₂O₃ Films Prepared by Halide Vapor Phase Epitaxy

by Eugene B. Yakimov, Alexander Y. Polyakov, Vladimir I. Nikolaev, Alexei I. Pechnikov, Mikhail P. Scheglov, Eugene E. Yakimov and Stephen J. Pearton

Nanomaterials 2023, 13(7), 1214; https://doi.org/10.3390/nano13071214 - 29 Mar 2023

Cited by 9 | Viewed by 1518

Abstract

In this study, the structural and electrical properties of orthorhombic κ-Ga₂O₃ films prepared using Halide Vapor Phase Epitaxy (HVPE) on AlN/Si and GaN/sapphire templates were studied. For κ-Ga₂O₃/AlN/Si structures, the formation of two-dimensional hole layers in [...] Read more.

In this study, the structural and electrical properties of orthorhombic κ-Ga₂O₃ films prepared using Halide Vapor Phase Epitaxy (HVPE) on AlN/Si and GaN/sapphire templates were studied. For κ-Ga₂O₃/AlN/Si structures, the formation of two-dimensional hole layers in the Ga₂O₃ was studied and, based on theoretical calculations, was explained by the impact of the difference in the spontaneous polarizations of κ-Ga₂O₃ and AlN. Structural studies indicated that in the thickest κ-Ga₂O₃/GaN/sapphire layer used, the formation of rotational nanodomains was suppressed. For thick (23 μm and 86 μm) κ-Ga₂O₃ films grown on GaN/sapphire, the good rectifying characteristics of Ni Schottky diodes were observed. In addition, deep trap spectra and electron beam-induced current measurements were performed for the first time in this polytype. These experiments show that the uppermost 2 µm layer of the grown films contains a high density of rather deep electron traps near E_c − 0.3 eV and E_c − 0.7 eV, whose presence results in the relatively high series resistance of the structures. The diffusion length of the excess charge carriers was measured for the first time in κ-Ga₂O₃. The film with the greatest thickness of 86 μm was irradiated with protons and the carrier removal rate was about 10 cm⁻¹, which is considerably lower than that for β-Ga₂O₃. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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7 pages, 3155 KiB

Open AccessEditor’s ChoiceArticle

Plasma Nitridation Effect on β-Ga₂O₃ Semiconductors

by Sunjae Kim, Minje Kim, Jihyun Kim and Wan Sik Hwang

Nanomaterials 2023, 13(7), 1199; https://doi.org/10.3390/nano13071199 - 28 Mar 2023

Cited by 2 | Viewed by 1665

Abstract

The electrical and optoelectronic performance of semiconductor devices are mainly affected by the presence of defects or crystal imperfections in the semiconductor. Oxygen vacancies are one of the most common defects and are known to serve as electron trap sites whose energy levels [...] Read more.

The electrical and optoelectronic performance of semiconductor devices are mainly affected by the presence of defects or crystal imperfections in the semiconductor. Oxygen vacancies are one of the most common defects and are known to serve as electron trap sites whose energy levels are below the conduction band (CB) edge for metal oxide semiconductors, including β-Ga₂O₃. In this study, the effects of plasma nitridation (PN) on polycrystalline β-Ga₂O₃ thin films are discussed. In detail, the electrical and optical properties of polycrystalline β-Ga₂O₃ thin films are compared at different PN treatment times. The results show that PN treatment on polycrystalline β-Ga₂O₃ thin films effectively diminish the electron trap sites. This PN treatment technology could improve the device performance of both electronics and optoelectronics. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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10 pages, 2744 KiB

Open AccessArticle

A Novel Method for Growing α-Ga₂O₃ Films Using Mist-CVD Face-to-face Heating Plates

by Yan Zuo, Qian Feng, Tao Zhang, Xusheng Tian, Wenji Li, Jiale Li, Chunfu Zhang, Jincheng Zhang and Yue Hao

Nanomaterials 2023, 13(1), 72; https://doi.org/10.3390/nano13010072 - 23 Dec 2022

Cited by 1 | Viewed by 2143

Abstract

In this paper, the method for growing α-Ga₂O₃ films on c-plane sapphire substrates using an inexpensive fine-channel mist-CVD face-to-face heating plate was investigated. Because high temperatures can result in reactor deformation, expensive AlN ceramics resistant to deformation are used as [...] Read more.

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

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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10 pages, 3070 KiB

Open AccessArticle

Tunable Optical Properties of Amorphous-Like Ga₂O₃ Thin Films Deposited by Electron-Beam Evaporation with Varying Oxygen Partial Pressures

by Shijie Li, Chen Yang, Jin Zhang, Linpeng Dong, Changlong Cai, Haifeng Liang and Weiguo Liu

Nanomaterials 2020, 10(9), 1760; https://doi.org/10.3390/nano10091760 - 6 Sep 2020

Cited by 18 | Viewed by 3009

Abstract

Ga₂O₃ thin films were fabricated by the electron-beam evaporation technique at a varying oxygen partial pressure from 0 to 2.0 × 10⁻² Pa. The effect of oxygen partial pressure on the crystalline structure and optical properties of the Ga [...] Read more.

Ga₂O₃ thin films were fabricated by the electron-beam evaporation technique at a varying oxygen partial pressure from 0 to 2.0 × 10⁻² Pa. The effect of oxygen partial pressure on the crystalline structure and optical properties of the Ga₂O₃ films was analyzed using sophisticated techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet-visible spectroscopy and a laser-induced damage test system. The correlation between the oxygen partial pressure and the film’s properties in optics and materials were investigated. XRD and Raman revealed that all films were amorphous in spite of applying a varying oxygen partial pressure. With the change of oxygen partial pressure, XPS data indicated that the content of oxygen in the Ga₂O₃ films could be broadly modulable. As a result, a changeable refractive index of the Ga₂O₃ film is realizable and a variable blue-shift of absorption edges in transmittance spectra of the films is achievable. Moreover, the damage threshold value varied from 0.41 to 7.51 J/cm² according to the rise of oxygen partial pressure. These results demonstrated that the optical properties of Ga₂O₃ film can be broadly tunable by controlling the oxygen content in the film. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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9 pages, 3923 KiB

Open AccessArticle

Catalyst-Assisted Large-Area Growth of Single-Crystal β-Ga₂O₃ Nanowires on Sapphire Substrates by Metal–Organic Chemical Vapor Deposition

by Chunyang Jia, Dae-Woo Jeon, Jianlong Xu, Xiaoyan Yi, Ji-Hyeon Park and Yiyun Zhang

Nanomaterials 2020, 10(6), 1031; https://doi.org/10.3390/nano10061031 - 28 May 2020

Cited by 14 | Viewed by 3356

Abstract

In this work, we have achieved synthesizing large-area high-density β-Ga₂O₃ nanowires on c-plane sapphire substrate by metal–organic chemical vapor deposition assisted with Au nanocrystal seeds as catalysts. These nanowires exhibit one-dimensional structures with Au nanoparticles on the top of [...] Read more.

In this work, we have achieved synthesizing large-area high-density β-Ga₂O₃ nanowires on c-plane sapphire substrate by metal–organic chemical vapor deposition assisted with Au nanocrystal seeds as catalysts. These nanowires exhibit one-dimensional structures with Au nanoparticles on the top of the nanowires with lengths exceeding 6 μm and diameters ranging from ~50 to ~200 nm. The β-Ga₂O₃ nanowires consist of a single-crystal monoclinic structure, which exhibits strong (

\bar{2}

01) orientation, confirmed by transmission electronic microscopy and X-ray diffraction analysis. The PL spectrum obtained from these β-Ga₂O₃ nanowires exhibits strong emissions centered at ~360 and ~410 nm, respectively. The energy band gap of the β-Ga₂O₃ nanowires is estimated to be ~4.7 eV based on an optical transmission test. A possible mechanism for the growth of β-Ga₂O₃ nanowires is also presented. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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Review

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62 pages, 13237 KiB

Open AccessReview

A Review on Gallium Oxide Materials from Solution Processes

by Jung-Lung Chiang, Bharath Kumar Yadlapalli, Mu-I Chen and Dong-Sing Wuu

Nanomaterials 2022, 12(20), 3601; https://doi.org/10.3390/nano12203601 - 14 Oct 2022

Cited by 18 | Viewed by 6381

Abstract

Gallium oxide (Ga₂O₃) materials can be fabricated via various methods or processes. It is often mentioned that it possesses different polymorphs (α-, β-, γ-, δ- and ε-Ga₂O₃) and excellent physical and chemical properties. The basic [...] Read more.

Gallium oxide (Ga₂O₃) materials can be fabricated via various methods or processes. It is often mentioned that it possesses different polymorphs (α-, β-, γ-, δ- and ε-Ga₂O₃) and excellent physical and chemical properties. The basic properties, crystalline structure, band gap, density of states, and other properties of Ga₂O₃ will be discussed in this article. This article extensively discusses synthesis of pure Ga₂O₃, co-doped Ga₂O₃ and Ga₂O₃-metal oxide composite and Ga₂O₃/metal oxide heterostructure nanomaterials via solution-based methods mainly sol-gel, hydrothermal, chemical bath methods, solvothermal, forced hydrolysis, reflux condensation, and electrochemical deposition methods. The influence of the type of precursor solution and the synthesis conditions on the morphology, size, and properties of final products is thoroughly described. Furthermore, the applications of Ga₂O₃ will be introduced and discussed from these solution processes, such as deep ultraviolet photodetector, gas sensors, pH sensors, photocatalytic and photodegradation, and other applications. In addition, research progress and future outlook are identified. Full article

(This article belongs to the Special Issue Ga₂O₃-Based Nanomaterials)

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