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Accumulation and removal of Si impurities on β -Ga2O3 arising from ambient air exposure

https://doi.org/10.1063/5.0191280

McCandless, J P; Gorsak, C A; Protasenko, V; Schlom, D G; Thompson, Michael O; Xing, H G; Jena, D; Nair, H P (March 2024, Applied Physics Letters)

Here, we report that a source of Si impurities commonly observed on (010) β-Ga2O3 is from exposure of the surface to air. Moreover, we find that a 15 min hydrofluoric acid (HF) (49%) treatment reduces the Si density by approximately 1 order of magnitude on (010) β-Ga2O3 surfaces. This reduction in Si is critical for the elimination of the often observed parasitic conducting channel, which negatively affects transport properties and lateral transistor performance. After the HF treatment, the sample must be immediately put under vacuum, for the Si fully returns within 10 min of additional air exposure. Finally, we demonstrate that performing a 30 min HF (49%) treatment on the substrate before growth has no deleterious effect on the structure or on the epitaxy surface after subsequent Ga2O3 growth.
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Growth of α-Ga ₂ O ₃ on α-Al ₂ O ₃ by conventional molecular-beam epitaxy and metal–oxide-catalyzed epitaxy

https://doi.org/10.35848/1347-4065/acbe04

McCandless, J. P.; Rowe, D.; Pieczulewski, N.; Protasenko, V.; Alonso-Orts, M.; Williams, M. S.; Eickhoff, M.; Xing, H. G.; Muller, D. A.; Jena, D.; et al (March 2023, Japanese Journal of Applied Physics)

Abstract We report the growth of α -Ga 2 O 3 on m -plane α -Al 2 O 3 by conventional plasma-assisted molecular-beam epitaxy and In-mediated metal–oxide-catalyzed epitaxy (MOCATAXY). We report a growth rate diagram for α -Ga 2 O 3 ( 10 1 ¯ 0 ), and observe (i) a growth rate increase, (ii) an expanded growth window, and (iii) reduced out-of-lane mosaic spread when MOCATAXY is employed for the growth of α -Ga 2 O 3 . Through the use of In-mediated catalysis, growth rates over 0.2 μ m h −1 and rocking curves with full width at half maxima of Δ ω ≈ 0.45° are achieved. Faceting is observed along the α -Ga 2 O 3 film surface and explored through scanning transmission electron microscopy.
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Controlled Si doping of β -Ga ₂ O ₃ by molecular beam epitaxy

https://doi.org/10.1063/5.0101132

McCandless, J. P.; Protasenko, V.; Morell, B. W.; Steinbrunner, E.; Neal, A. T.; Tanen, N.; Cho, Y.; Asel, T. J.; Mou, S.; Vogt, P.; et al (August 2022, Applied Physics Letters)

We report controlled silicon doping of Ga 2 O 3 grown in plasma-assisted molecular beam epitaxy. Adding an endplate to the Si effusion cell enables the control of the mobile carrier density, leading to over 5-orders of magnitude change in the electrical resistivity. Room temperature mobilities [Formula: see text] are achieved, with a peak value [Formula: see text] at a doping density of low-[Formula: see text]. Temperature-dependent Hall effect measurements exhibit carrier freeze out for samples doped below the Mott criterion. A mobility of [Formula: see text] is observed at [Formula: see text].
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Thermal stability of epitaxial α -Ga ₂ O ₃ and (Al,Ga) ₂ O ₃ layers on m-plane sapphire

https://doi.org/10.1063/5.0064278

McCandless, J. P.; Chang, C. S.; Nomoto, K.; Casamento, J.; Protasenko, V.; Vogt, P.; Rowe, D.; Gann, K.; Ho, S. T.; Li, W.; et al (August 2021, Applied Physics Letters)

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