The development of novel ultra-wide bandgap (UWBG) materials requires precise understanding of the atomic level structural origins that give rise to their important properties. We study the aluminum atom incorporation, defect formation, and their relationships with phase stability in β-(Al_xGa_1−x)₂O₃ films, a promising candidate for UWBG applications, to explain atomic scale structural characteristics and properties using a combination of quantitative scanning transmission electron microscopy (STEM) and density functional theory (DFT). Our STEM analysis indicates that ∼54% of the incorporated Al substitutes on the octahedrally coordinated Ga₂ site in a series of films grown with different techniques and alloy concentrations. DFT calculations show that, while Al energetically prefers the octahedral site, surface reconstructions and kinetic limitations during the epitaxial growth are responsible for Al occupying both octahedral and tetrahedral sites in (Al_xGa_1−x)₂O₃, ultimately limiting the stability of the β-phase at x < ∼50%. Local heterogeneity of composition results in the formation of a planar defect, affecting the stability of the β-phase. The similarity of such inclusions to the metastable γ-phase is discussed.

中文翻译：

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β-(AlxGa1−x)2O3 薄膜中铝掺入、缺陷和相稳定性的原子尺度研究

新型超宽带隙 (UWBG) 材料的开发需要精确了解导致其重要特性的原子级结构起源。我们研究了β -(Al _x Ga _1-x ) ₂ O ₃薄膜中铝原子的掺入、缺陷形成及其与相稳定性的关系，β- (Al _x Ga _1-x ) ₂ O ₃薄膜是 UWBG 应用的有希望的候选者，以使用组合来解释原子级结构特征和性能定量扫描透射电子显微镜 (STEM) 和密度泛函理论 (DFT)。我们的 STEM 分析表明，约 54% 的掺入 Al 替代了八面体配位的 Ga ₂位点在一系列使用不同技术和合金浓度生长的薄膜中。DFT 计算表明，虽然 Al 在能量上更喜欢八面体位点，但外延生长过程中的表面重建和动力学限制是导致 Al 在 (Al _x Ga _1-x ) ₂ O _{3 中}同时占据八面体和四面体位点的原因，最终限制了其稳定性x < 50%处的β相。成分的局部异质性导致形成平面缺陷，影响β相的稳定性。讨论了这种夹杂物与亚稳态γ相的相似性。