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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. 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)
3. 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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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. Band Alignment of Al ₂ O ₃ on α-(Al _x Ga _1-x ) ₂ O ₃

   https://doi.org/10.1149/2162-8777/ac546f  

   Xia, Xinyi; Al-Mamun, Nahid Sultan; Fares, Chaker; Haque, Aman; Ren, Fan; Hassa, Anna; von Wenckstern, Holger; Grundmann, Marius; Pearton, S. J. (February 2022, ECS Journal of Solid State Science and Technology)

   X Ray Photoelectron Spectroscopy was used to measure valence band offsets for Al 2 O 3 deposited by Atomic Layer Deposition on α -(Al x Ga 1-x ) 2 O 3 alloys over a wide range of Al contents, x, from 0.26–0.74, corresponding to a bandgap range from 5.8–7 eV. These alloys were grown by Pulsed Laser Deposition. The band alignments were type I (nested) at x <0.5, with valence band offsets 0.13 eV for x = 0.26 and x = 0.46. At higher Al contents, the band alignment was a staggered alignment, with valence band offsets of − 0.07 eV for x = 0.58 and −0.17 for x = 0.74, ie. negative valence band offsets in both cases. The conduction band offsets are also small at these high Al contents, being only 0.07 eV at x = 0.74. The wide bandgap of the α -(Al x Ga 1-x ) 2 O 3 alloys makes it difficult to find dielectrics with nested band alignments over the entire composition range. 

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