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1. Structural and electronic properties of Ga ₂ O ₃ -Al ₂ O ₃ alloys

   https://doi.org/10.1063/1.5036991  

   Peelaers, Hartwin; Varley, Joel B.; Speck, James S.; Van de Walle, Chris G. (June 2018, Applied Physics Letters)
2. A review of band structure and material properties of transparent conducting and semiconducting oxides: Ga ₂ O ₃ , Al ₂ O ₃ , In ₂ O ₃ , ZnO, SnO ₂ , CdO, NiO, CuO, and Sc ₂ O ₃

   https://doi.org/10.1063/5.0078037  

   Spencer, Joseph A.; Mock, Alyssa L.; Jacobs, Alan G.; Schubert, Mathias; Zhang, Yuhao; Tadjer, Marko J. (March 2022, Applied Physics Reviews)

   This Review highlights basic and transition metal conducting and semiconducting oxides. We discuss their material and electronic properties with an emphasis on the crystal, electronic, and band structures. The goal of this Review is to present a current compilation of material properties and to summarize possible uses and advantages in device applications. We discuss Ga 2 O 3 , Al 2 O 3 , In 2 O 3 , SnO 2 , ZnO, CdO, NiO, CuO, and Sc 2 O 3 . We outline the crystal structure of the oxides, and we present lattice parameters of the stable phases and a discussion of the metastable polymorphs. We highlight electrical properties such as bandgap energy, carrier mobility, effective carrier masses, dielectric constants, and electrical breakdown field. Based on literature availability, we review the temperature dependence of properties such as bandgap energy and carrier mobility among the oxides. Infrared and Raman modes are presented and discussed for each oxide providing insight into the phonon properties. The phonon properties also provide an explanation as to why some of the oxide parameters experience limitations due to phonon scattering such as carrier mobility. Thermal properties of interest include the coefficient of thermal expansion, Debye temperature, thermal diffusivity, specific heat, and thermal conductivity. Anisotropy is evident in the non-cubic oxides, and its impact on bandgap energy, carrier mobility, thermal conductivity, coefficient of thermal expansion, phonon modes, and carrier effective mass is discussed. Alloys, such as AlGaO, InGaO, (Al x In y Ga 1− x− y ) 2 O 3 , ZnGa 2 O 4 , ITO, and ScGaO, were included where relevant as they have the potential to allow for the improvement and alteration of certain properties. This Review provides a fundamental material perspective on the application space of semiconducting oxide-based devices in a variety of electronic and optoelectronic applications. 

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3. 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)
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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