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1. MOCVD Growth of β-Ga ₂ O ₃ on (001) Ga ₂ O ₃ Substrates

   https://doi.org/10.1021/acs.cgd.4c00060  

   Meng, Lingyu; Yu, Dongsu; Huang, Hsien-Lien; Chae, Chris; Hwang, Jinwoo; Zhao, Hongping (May 2024, Crystal Growth & Design)
2. Trapping of multiple H atoms at the Ga(1) vacancy in β -Ga ₂ O ₃

   https://doi.org/10.1063/5.0024269  

   Fowler, W. Beall; Stavola, Michael; Qin, Ying; Weiser, Philip (October 2020, Applied Physics Letters)

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3. Influence of Polymorphism on the Electronic Structure of Ga ₂ O ₃

   https://doi.org/10.1021/acs.chemmater.0c02465  

   Swallow, Jack E.; Vorwerk, Christian; Mazzolini, Piero; Vogt, Patrick; Bierwagen, Oliver; Karg, Alexander; Eickhoff, Martin; Schörmann, Jörg; Wagner, Markus R.; Roberts, Joseph W.; et al (September 2020, Chemistry of Materials)

   The search for new wide-band-gap materials is intensifying to satisfy the need for more advanced and energy-efficient power electronic devices. Ga2O3 has emerged as an alternative to SiC and GaN, sparking a renewed interest in its fundamental properties beyond the main β-phase. Here, three polymorphs of Ga2O3, α, β, and ε, are investigated using X-ray diffraction, X-ray photoelectron and absorption spectroscopy, and ab initio theoretical approaches to gain insights into their structure–electronic structure relationships. Valence and conduction electronic structure as well as semicore and core states are probed, providing a complete picture of the influence of local coordination environments on the electronic structure. State-of-the-art electronic structure theory, including all-electron density functional theory and many-body perturbation theory, provides detailed understanding of the spectroscopic results. The calculated spectra provide very accurate descriptions of all experimental spectra and additionally illuminate the origin of observed spectral features. This work provides a strong basis for the exploration of the Ga2O3 polymorphs as materials at the heart of future electronic device generations. 

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4. Thermal Stability of Transparent ITO/n-Ga ₂ O ₃ /n+-Ga ₂ O ₃ /ITO Rectifiers

   https://doi.org/10.1149/2162-8777/ac3ace  

   Xia, Xinyi; Xian, Minghan; Ren, Fan; Rasel, Md Abu; Haque, Aman; Pearton, S. J. (November 2021, ECS Journal of Solid State Science and Technology)

   The thermal stability of n/n + β -Ga 2 O 3 epitaxial layer/substrate structures with sputtered ITO on both sides to act as rectifying contacts on the lightly doped layer and Ohmic on the heavily doped substrate is reported. The resistivity of the ITO deposited separately on Si decreased from 1.83 × 10 −3 Ω.cm as-deposited to 3.6 × 10 −4 Ω.cm after 300 °C anneal, with only minor reductions at higher temperatures (2.8 × 10 −4 Ω.cm after 600 °C anneals). The Schottky barrier height also decreased with annealing, from 0.98 eV in the as-deposited samples to 0.85 eV after 500 °C annealing. The reverse breakdown voltage exhibited a negative temperature coefficient of −0.46 V.C −1 up to an annealing temperature of 400 °C and degraded faster at higher temperatures. Transmission Electron Microscopy showed significant reaction at the ITO and Ga 2 O 3 interface above 300 °C, with a very degraded contact stack after annealing at 500 °C. 

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5. Initial nucleation of metastable γ-Ga ₂ O ₃ during sub-millisecond thermal anneals of amorphous Ga ₂ O ₃

   https://doi.org/10.1063/5.0087093  

   Gann, Katie R.; Chang, Celesta S.; Chang, Ming-Chiang; Sutherland, Duncan R.; Connolly, Aine B.; Muller, David A.; van Dover, Robert B.; Thompson, Michael O. (August 2022, Applied Physics Letters)

   Beta-phase gallium oxide ([Formula: see text]-Ga 2 O 3 ) is a promising semiconductor for high frequency, high temperature, and high voltage applications. In addition to the [Formula: see text]-phase, numerous other polymorphs exist and understanding the competition between phases is critical to control practical devices. The phase formation sequence of Ga 2 O 3 , starting from amorphous thin films, was determined using lateral-gradient laser spike annealing at peak temperatures of 500–1400 °C on 400 μs to 10 ms timescales, with transformations characterized by optical microscopy, x-ray diffraction, and transmission electron microscopy (TEM). The resulting phase processing map showed the [Formula: see text]-phase, a defect-spinel structure, first nucleating under all annealing times for temperatures from 650 to 800 °C. The cross-sectional TEM at the onset of the [Formula: see text]-phase formation showed nucleation near the film center with no evidence of heterogeneous nucleation at the interfaces. For temperatures above 850 °C, the thermodynamically stable [Formula: see text]-phase was observed. For anneals of 1–4 ms and temperatures below 1200 °C, small randomly oriented grains were observed. Large grains were observed for anneals below 1 ms and above 1200 °C, with anneals above 4 ms and 1200 °C resulting in textured films. The formation of the [Formula: see text]-phase prior to [Formula: see text]-phase, coupled with the observed grain structure, suggests that the [Formula: see text]-phase is kinetically preferred during thermal annealing of amorphous films, with [Formula: see text]-phase subsequently forming by nucleation at higher temperatures. The low surface energy of the [Formula: see text]-phase implied by these results suggests an explanation for the widely observed [Formula: see text]-phase inclusions in [Formula: see text]-phase Ga 2 O 3 films grown by a variety of synthesis methods. 

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