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AlScN High Electron Mobility Transistors: Integrating High Piezoelectric, High K Dielectric, and Ferroelectric Functionality

https://doi.org/10.1109/BCICTS54660.2023.10310921

Casamento, Joseph; Nomoto, Kazuki; Nguyen, Thai-Son; Lee, Hyunjea; Savant, Chandrasekhar; Li, Lei; Hickman, Austin; Maeda, Takuya; Shao, Yu-Tsun; Encomendero, Jimy; et al (October 2023, IEEE)

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Strong effect of scandium source purity on chemical and electronic properties of epitaxial ScxAl1 − xN/GaN heterostructures

https://doi.org/10.1063/5.0054522

Casamento, Joseph; Lee, Hyunjea; Chang, Celesta_S; Besser, Matthew_F; Maeda, Takuya; Muller, David_A; Xing, Huili_Grace; Jena, Debdeep (September 2021, APL Materials)

Epitaxial multilayer heterostructures of ScxAl1−xN/GaN with Sc contents x = 0.11–0.45 are found to exhibit significant differences in structural quality, chemical impurity levels, and electronic properties depending on the starting Sc source impurity levels. A higher purity source leads to a 2–3 orders of magnitude reduction in the carbon, oxygen, and fluorine unintentional doping densities in MBE-grown ScxAl1−xN/GaN multilayers. Electrical measurements of ScxAl1−xN/n+GaN single heterostructure barriers show a 5–7 orders of magnitude reduction in the electrical leakage for films grown with a higher purity Sc source at most Sc contents. The measured chemical and electrical properties of epitaxial ScxAl1−xN highlight the importance of the starting Sc source material purity for epitaxial device applications that need these highly piezoelectric and/or ferroelectric transition-metal nitride alloys.
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Epitaxial Sc _x Al ₁₋ _x N on GaN exhibits attractive high-K dielectric properties

https://doi.org/10.1063/5.0075636

Casamento, Joseph; Lee, Hyunjea; Maeda, Takuya; Gund, Ved; Nomoto, Kazuki; van Deurzen, Len; Turner, Wesley; Fay, Patrick; Mu, Sai; Van de Walle, Chris G.; et al (April 2022, Applied Physics Letters)

Epitaxial Sc_xAl₁₋_xN thin films of ∼100 nm thickness grown on metal polar GaN substrates are found to exhibit significantly enhanced relative dielectric permittivity (ε_r) values relative to AlN. ε_rvalues of ∼17–21 for Sc mole fractions of 17%–25% ( x = 0.17–0.25) measured electrically by capacitance–voltage measurements indicate that Sc_xAl₁₋_xN has the largest relative dielectric permittivity of any existing nitride material. Since epitaxial Sc_xAl₁₋_xN layers deposited on GaN also exhibit large polarization discontinuity, the heterojunction can exploit the in situ high-K dielectric property to extend transistor operation for power electronics and high-speed microwave applications.
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