β-Ga₂O₃ is a promising ultra-wide bandgap semiconductor whose properties can be further enhanced by alloying with Al. Here, using atomic-resolution scanning transmission electron microscopy, we find the thermodynamically unstable γ-phase is a ubiquitous structural defect in both β-(Al_xGa_1−x)₂O₃ films and doped β-Ga₂O₃ films grown by molecular beam epitaxy. For undoped β-(Al_xGa_1−x)₂O₃ films, we observe γ-phase inclusions between nucleating islands of the β-phase at lower growth temperatures (∼500–600 °C). In doped β-Ga₂O₃, a thin layer of the γ-phase is observed on the surfaces of films grown with a wide range of n-type dopants and dopant concentrations. The thickness of the γ-phase layer was most strongly correlated with the growth temperature, peaking at about 600 °C. Ga interstitials are observed in the β-phase, especially near the interface with the γ-phase. By imaging the same region of the surface of a Sn-doped β-(Al_xGa_1−x)₂O₃ after ex situ heating up to 400 °C, a γ-phase region is observed to grow above the initial surface, accompanied by a decrease in Ga interstitials in the β-phase. This suggests that the diffusion of Ga interstitials toward the surface is likely the mechanism for growth of the surface γ-phase and more generally that the more-open γ-phase may offer diffusion pathways to be a kinetically favored and early forming phase in the growth of Ga₂O₃. However, more modeling and simulation of the γ-phase and the interstitials are needed to understand the energetics and kinetics, the impact on electronic properties, and how to control them.

中文翻译：

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γ相夹杂物作为合金化β-(AlxGa1-x)2O3和掺杂β-Ga2O3薄膜中常见的结构缺陷

β -Ga ₂ O ₃是一种很有前途的超宽带隙半导体，通过与Al合金化可以进一步增强其性能。在这里，使用原子分辨率扫描透射电子显微镜，我们发现热力学不稳定的γ相是β -(Al _x Ga _{1− x} ) ₂ O ₃薄膜和掺杂的β -Ga ₂ O ₃薄膜中普遍存在的结构缺陷通过分子束外延。对于未掺杂的β -(Al _x Ga _{1− x} ) ₂ O ₃对于薄膜，我们在较低的生长温度（~500-600°C）下观察到β相成核岛之间的γ相夹杂物。在掺杂的β -Ga ₂ O _{3 中}，在以宽范围的 n 型掺杂剂和掺杂剂浓度生长的薄膜表面上观察到γ相薄层。γ相层的厚度与生长温度的相关性最强，在 600 °C 左右达到峰值。在β相中观察到 Ga 间隙，尤其是在与γ相的界面附近。通过对掺杂 Sn 的β -(Al _x Ga_{1- x} ) ₂ O ₃在异位加热至 400 °C 后，观察到γ相区域在初始表面上方生长，伴随着β相中Ga 间隙的减少。这表明 Ga 间隙向表面的扩散可能是表面γ相生长的机制，更一般地说，更开放的γ相可能提供扩散途径，成为生长中动力学有利的早期形成阶段的Ga ₂ O ₃。然而，更多的γ建模和模拟需要-相和间隙来了解能量学和动力学、对电子特性的影响以及如何控制它们。