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β-Ga2O3: Growth (Bulk, Thin Film, Epitaxy)...
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β-Ga2O3: Growth (Bulk, Thin Film, Epitaxy) and Physical Properties

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Materials for Energy Applications".

Deadline for manuscript submissions: 30 June 2024 | Viewed by 5360

Special Issue Editors

Dr. Sridharan Moorthy Babu

E-Mail Website
Guest Editor
Crystal Growth Centre, Anna University, Chennai 600025, Tamilnadu, India
Interests: bulk crystals growth; β-Ga2O3; floating zone method; epitaxial growth
Prof. Dr. Fan Ren

E-Mail Website
Guest Editor
Department of Chemical Engineering, University of Florida, Gainesville, FL 32611, USA
Interests: β-Ga2O3; oxide-based optical and electronic devices; transistors; ultra-wide bandgap semiconductor; Schottky diode; bulk crystals

Special Issue Information

Dear Colleagues,

Beta gallium oxide (β-Ga2O3) is an exciting wide-bandgap semiconductor with tremendous potential across various technological applications. Its unique properties make it highly suitable for power electronics, solar-blind UV detectors, sensor applications (such as explosives detection), and even as substrates for laser diodes. This Special Issue focuses on the growth aspects of β-Ga2O3, including bulk crystals, thin films as well as epitaxial layers with suitable processes. Melt growth techniques Czochralski, Bridgman, floating zone, edge-defined film-fed growth, and Veneuil can be used for bulk crystal growth. Many thin film preparation methods like pulsed laser deposition, spin coating, sputtering, e-beam evaporation, and sol–gel synthesis have been successfully reported. Epitaxial processes, including MOVPE, MBE, and Mist-CVD, have also shown promising results in the literature. The growth of beta gallium oxide (bulk, thin films, epitaxy) encounters many technological challenges and needs significant attention to be addressed for scientific or technical investigations in detail.

Moreover, the Special Issue aims to delve into optimizing the physical properties of β-Ga2O3 for diverse applications. This encompasses comprehensive investigations into the structural, optical, electrical, and spectroscopic properties of both pure and doped β-Ga2O3 materials. Understanding these properties is crucial for tailoring β-Ga2O3 to specific device structures and maximizing performance.

The scope of this Special Issue extends beyond conventional research boundaries, offering a platform to explore emerging trends in the growth of β-Ga2O3 and its physical properties. It encourages the submission of experimental studies, theoretical investigations, and innovative approaches that shed light on the fundamental principles underlying the growth processes and highlight the unique characteristics of β-Ga2O3. By bringing together cutting-edge research, this Special Issue aims to propel the field forward and inspire further advancements in the realm of β-Ga2O3-based technologies. The potential topics of interest include but are not limited to:

  • Experimental aspects of β-Ga2O3 Bulk crystal growth;
  • β-Ga2O3 thin film growth;
  • Epitaxial growth of β-Ga2O3;
  • Material and physical properties of β-Ga2O3 (bulk, thin film, epitaxy);
  • Structural, optical, electrical, and spectroscopic properties of pure and doped β-Ga2O3;
  • Device structures and role of physical properties of β-Ga2O3 (bulk, thin films, epitaxy).

Dr. Sridharan Moorthy Babu
Prof. Dr. Fan Ren
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • β-Ga2O3
  • bulk crystal growth
  • thin film growth
  • epitaxy growth
  • physical, structural, optical, electrical, spectroscopic properties
  • wide-bandgap semiconductor
  • power electronics
  • solar-blind UV detectors
  • sensor applications
  • melt growth techniques
  • Czochralski method
  • Bridgman method
  • floating zone method
  • edge-defined film-fed growth method
  • Veneuil method

Published Papers (4 papers)

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Research

12 pages, 5257 KiB  
Article
β-Ga2O3 Schottky Barrier Diode with Ion Beam Sputter-Deposited Semi-Insulating Layer
by Nikita N. Yakovlev, Aleksei V. Almaev, Bogdan O. Kushnarev, Maksim G. Verkholetov, Maksim V. Poliakov and Mikhail M. Zinovev
Crystals 2024, 14(2), 123; https://doi.org/10.3390/cryst14020123 - 26 Jan 2024
Viewed by 876
Abstract
Vertical Schottky barrier diodes based on an ion beam sputter (IBS)-deposited β-Ga2O3 film on a single-crystalline (2¯01) unintentionally doped (UID) β-Ga2O3 with a Ni contact were developed. To form ohmic Ti/Ni contacts, the IBS-Ga [...] Read more.
Vertical Schottky barrier diodes based on an ion beam sputter (IBS)-deposited β-Ga2O3 film on a single-crystalline (2¯01) unintentionally doped (UID) β-Ga2O3 with a Ni contact were developed. To form ohmic Ti/Ni contacts, the IBS-Ga2O3/UID β-Ga2O3 structures were wet-etched, and an indium tin oxide (ITO) intermediate semiconductor layer (ISL) was deposited on the opposite surface of the UID β-Ga2O3. The IBS-deposited Ga2O3 layer was polycrystalline and semi-insulating. Low leakage currents, rectification ratios of 3.9 × 108 arb. un. and 3.4 × 106 arb. un., ideality factors of 1.43 and 1.24, Schottky barrier heights of 1.80 eV and 1.67 eV as well as breakdown voltages of 134 V and 180 V were achieved for diodes without and with ITO-ISL, respectively. The surface area of the IBS-Ga2O3 film acted as a thin dielectric layer and, together with the preliminary wet etching, provided low leakage currents and relatively high Schottky barrier heights. Diodes with a Schottky barrier based on a Ni/IBS-deposited Ga2O3 film contact were demonstrated for the first time. Full article
(This article belongs to the Special Issue β-Ga2O3: Growth (Bulk, Thin Film, Epitaxy) and Physical Properties)
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12 pages, 4945 KiB  
Article
Influence of Active Afterheater in the Crystal Growth of Gallium Oxide via Edge-Defined Film-Fed Growing Method
by Woon-Hyeon Jeong, Su-Min Choi, Su-Min Lim, Yun-Ji Shin, Si-Young Bae, Jin-Ki Kang, Won-Jae Lee, Se-Hun Kwon and Seong-Min Jeong
Crystals 2023, 13(11), 1591; https://doi.org/10.3390/cryst13111591 - 17 Nov 2023
Viewed by 951
Abstract
In this study, we explored the effect of an active afterheater on the growth of gallium oxide single crystals using the EFG method. We analyzed the temperature distribution of the crystal under the growing process through multiphysics simulations of the models with and [...] Read more.
In this study, we explored the effect of an active afterheater on the growth of gallium oxide single crystals using the EFG method. We analyzed the temperature distribution of the crystal under the growing process through multiphysics simulations of the models with and without an active afterheater and investigated the morphology of crystals by applying each model to real experimental growths. The afterheater is a component in the growing furnace that activates radiant heat transfer, and its performance depends on its location, size, material, and shape. The simulation results showed that the afterheater applied in this study was found to be effective in obtaining good temperature distribution in the reactor. Through experimental crystal growth corresponding to the simulation approaches, it was confirmed that an appropriate afterheater reduces thermal stress at the growth front and provides a thermal annealing effect on the post-grown crystals during the growing process to improve crystal quality. Full article
(This article belongs to the Special Issue β-Ga2O3: Growth (Bulk, Thin Film, Epitaxy) and Physical Properties)
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25 pages, 2462 KiB  
Article
Impact of Hydrogen Plasma on Electrical Properties and Deep Trap Spectra in Ga2O3 Polymorphs
by Alexander Y. Polyakov, Eugene B. Yakimov, Vladimir I. Nikolaev, Alexei I. Pechnikov, Andrej V. Miakonkikh, Alexander Azarov, In-Hwan Lee, Anton A. Vasilev, Anastasiia I. Kochkova, Ivan V. Shchemerov, Andrej Kuznetsov and Stephen J. Pearton
Crystals 2023, 13(9), 1400; https://doi.org/10.3390/cryst13091400 - 20 Sep 2023
Cited by 4 | Viewed by 1218
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue β-Ga2O3: Growth (Bulk, Thin Film, Epitaxy) and Physical Properties)
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12 pages, 3628 KiB  
Article
The Optimization of NiO Doping, Thickness, and Extension in kV-Class NiO/Ga2O3 Vertical Rectifiers
by Chao-Ching Chiang, Jian-Sian Li, Hsiao-Hsuan Wan, Fan Ren and Stephen J. Pearton
Crystals 2023, 13(7), 1124; https://doi.org/10.3390/cryst13071124 - 19 Jul 2023
Cited by 2 | Viewed by 1091
Abstract
Ga2O3 heterojunction rectifiers have emerged as a novel candidate for various power conversion applications by using NiO as the solution on the p-type side. In this work, the optimized design of high-breakdown (1–7 kV), vertical geometry NiO/Ga2O3 [...] Read more.
Ga2O3 heterojunction rectifiers have emerged as a novel candidate for various power conversion applications by using NiO as the solution on the p-type side. In this work, the optimized design of high-breakdown (1–7 kV), vertical geometry NiO/Ga2O3 rectifiers was examined using the Silvaco TCAD simulator to determine the electric field distribution for different NiO parameters. The doping concentration (1017–1019 cm−3), thickness (10–70 nm) of the guard ring, and its extension beyond the anode (0–30 µm) are all important in determining where the device breakdown occurs. Spatially, this can vary from the edge of the bilayer NiO extension to directly at the periphery of the top contact, consistent with experimental results. This transition phenomenon is proven to be correlated with the depletion effect by monitoring the depletion width when ramping up the bias and the doping concentration. The breakdown voltage was also calculated as a function of NiO top and bottom layer thicknesses and the doping concentration under different critical breakdown fields, where the latter is determined by the material quality of the drift layer. Full article
(This article belongs to the Special Issue β-Ga2O3: Growth (Bulk, Thin Film, Epitaxy) and Physical Properties)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Review of thermal transport properties of β-Ga2O3 and its interfaces
Authors: Chung-Ping Ho; Saeed Siahchehrehghadikolaei; Jingjing Shi
Affiliation: Mechanical & Aerospace Engineering, University of Florida
Abstract: β-Ga2O3 is promising for applications in power electronics and radio frequency devices because of their exceptional electronic properties and capability for scalable and efficient growth. However, the heat dissipation of the corresponding devices will be limited by the ultra-low thermal conductivity of (AlxGa1-x)2O3 and Ga2O3 and the high thermal boundary resistance (TBR) across device heterojunctions. Previous studies showed that these devices could achieve high power density with double-side cooling strategies. Therefore, understanding the thermal transport properties in materials and across interfaces becomes very important. In this work, we comprehensively review the modeling and experimental works that reported thermal conductivity and thermal boundary conductance (TBC) in β-Ga2O3 and β-(AlxGa1-x)2O3. The strategy with lower thermal resistance in materials and across interfaces for better thermal management of devices is discussed and proposed.

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