We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow α-(AlxGa1−x)2O3 films on (110) sapphire substrates over the 0 < x < 0.95 range of aluminum content. In S-MBE, 99.98% of the gallium-containing molecular beam arrives at the substrate in a preoxidized form as gallium suboxide (Ga2O). This bypasses the rate-limiting step of conventional MBE for the growth of gallium oxide (Ga2O3) from a gallium molecular beam and allows us to grow fully epitaxial α-(AlxGa1−x)2O3 films at growth rates exceeding 1 µm/h and relatively low substrate temperature (Tsub = 605 ± 15 °C). The ability to grow α-(AlxGa1−x)2O3 over the nominally full composition range is confirmed by Vegard’s law applied to the x-ray diffraction data and by optical bandgap measurements with ultraviolet–visible spectroscopy. We show that S-MBE allows straightforward composition control and bandgap selection for α-(AlxGa1−x)2O3 films as the aluminum incorporation x in the film is linear with the relative flux ratio of aluminum to Ga2O. The films are characterized by atomic-force microscopy, x-ray diffraction, and scanning transmission electron microscopy (STEM). These α-(AlxGa1−x)2O3 films grown by S-MBE at record growth rates exhibit a rocking curve full width at half maximum of ≊ 12 arc secs, rms roughness <1 nm, and are fully commensurate for x ≥ 0.5 for 20–50 nm thick films. STEM imaging of the x = 0.78 sample reveals high structural quality and uniform composition. Despite the high structural quality of the films, our attempts at doping with silicon result in highly insulating films.

中文翻译：

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通过低氧化物分子束外延以 1 µm/h 外延生长 α-(AlxGa1−x)2O3

我们报道了使用低氧化物分子束外延（S-MBE）在（110）蓝宝石衬底上生长 α-（AlxGa1−x）2O3 薄膜，温度范围为 0 < 0 x <铝含量0.95范围。在 S-MBE 中，99.98% 的含镓分子束以低氧化镓 (Ga2O) 的预氧化形式到达基底。这绕过了传统 MBE 从镓分子束生长氧化镓 (Ga2O3) 的限速步骤，使我们能够以超过 1 µm/h 的生长速率完全外延生长 α-(AlxGa1−x)2O3 薄膜。基板温度低（Tsub = 605 ± 15 °C）。应用到 X 射线衍射数据的 Vegard 定律以及紫外可见光谱的光学带隙测量证实了在名义上完整成分范围内生长 α-(AlxGa1−x)2O3 的能力。我们表明，S-MBE 允许对 α-(AlxGa1−x)2O3 薄膜进行直接的成分控制和带隙选择，因为薄膜中铝的掺入量 x 与铝与 Ga2O 的相对通量比呈线性关系。这些薄膜通过原子力显微镜、X 射线衍射和扫描透射电子显微镜 (STEM) 进行表征。这些通过 S-MBE 以创纪录的生长速率生长的 α-(AlxGa1−x)2O3 薄膜表现出摇摆曲线半峰全宽≊ 12 角秒，均方根粗糙度 <1 nm，并且与 x ≥ 0.5 完全相称20–50 nm 厚的薄膜。 x = 0.78 样品的 STEM 成像显示出较高的结构质量和均匀的成分。尽管薄膜的结构质量很高，但我们对硅掺杂的尝试导致了高度绝缘的薄膜。