发表机构
Materials Science Center, National Laboratory of the Rockies; Metallurgical and Materials Engineering Department, Colorado School of Mines; Renewable and Sustainable Energy Institute, University of Colorado Boulder（洛基山国家实验室材料科学中心; 科罗拉多矿业学院冶金与材料工程系; 科罗拉多大学博尔德分校可再生与可持续能源研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究揭示了Cr$_2$O$_3$和NiO在Ga$_2$O$_3$衬底上的外延关系，发现(001)取向时形成倾斜22.5°的界面，并提出了基于氧亚晶格等价性的解释及系统表征方法。
AI 中文摘要
p型氧化物接触层如Cr$_2$O$_3$和NiO，在与n型单斜β-Ga$_2$O$_3$形成的pn异质结中，正引起越来越多的关注，这些异质结用于高功率电子器件及其他极端环境应用。然而，对其外延关系的科学理解仍不完整。在本工作中，我们研究了Cr$_2$O$_3$和NiO层与(001)和($\bar{2}$01)取向的Ga$_2$O$_3$衬底的外延关系。令人惊讶的是，我们发现，对于商业上最相关的(001)取向Ga$_2$O$_3$衬底，外延关系为Cr$_2$O$_3$ (0001)和NiO (111) $\parallel$ Ga$_2$O$_3$ (101)，两者均相对于衬底法线呈非直觉的$\chi$ = 22.5$^\circ$角度。我们将这一不寻常的发现解释为界面原子键合由这些Cr$_2$O$_3$和NiO极性表面取向与倾斜的Ga$_2$O$_3$ (101)的氧亚晶格等价性主导，而非与Ga$_2$O$_3$ (001)衬底表面平面。此外，我们确定了Cr$_2$O$_3$在($\bar{2}$01)取向Ga$_2$O$_3$上的面内取向为：Cr$_2$O$_3$ $[12\bar{3}0]$ $\parallel$ Ga$_2$O$_3$ $[010]$，具有两个面内旋转畴。界面建模证实了Cr$_2$O$_3$/($\bar{2}$01) Ga$_2$O$_3$的面内取向，并表明应变O终止的Ga$_2$O$_3$ ($\bar{2}$01)表面与Cr$_2$O$_3$ (0001)具有最低的界面能。除了确定Cr$_2$O$_3$和NiO在Ga$_2$O$_3$上的具体外延关系外，本工作还为涉及晶体对称性显著不同的材料的异质界面提供了系统性的明确结构表征方法。
英文摘要
p-type oxide contact layers such as Cr$_2$O$_3$ and NiO are attracting increasing interest in pn-heterojunctions with n-type monoclinic $β$-Ga$_2$O$_3$ for high-power electronic devices and other extreme environment applications. However, scientific understanding of their epitaxial relationships remains incomplete. In this work we investigate the epitaxial relation of Cr$_2$O$_3$ and NiO layers to (001) and ($\bar{2}$01) out-of-plane oriented Ga$_2$O$_3$ substrates. Surprisingly, we find that, for the most commercially relevant (001)-orientation of the Ga$_2$O$_3$ substrate, the epitaxial relationships are Cr$_2$O$_3$ (0001) and NiO (111) $\parallel$ Ga$_2$O$_3$ (101), both at the non-intuitive $χ$ = 22.5 $^\circ$ angle with respect to the substrate normal. We explain this unusual discovery by the interfacial atomistic bonding dominated by oxygen sublattice equivalence of these Cr$_2$O$_3$ and NiO polar surface orientations to the tilted Ga$_2$O$_3$ (101), rather than Ga$_2$O$_3$ (001) substrate surface planes. Furthermore, we assign the in-plane orientation for Cr$_2$O$_3$ on ($\bar{2}$01)-oriented Ga$_2$O$_3$ as: Cr$_2$O$_3$ $[12\bar{3}0]$ $\parallel$ Ga$_2$O$_3$ $[010]$ with two in-plane rotational domains. Interface modeling confirms the in-plane orientation for Cr$_2$O$_3$/$(\bar{2}01)$ Ga$_2$O$_3$ and shows that strained O-terminated Ga$_2$O$_3$ $(\bar{2}01)$ surfaces have the lowest interfacial energy with Cr$_2$O$_3$ (0001). Beyond establishing the specific epitaxial relationships for Cr$_2$O$_3$ and NiO on Ga$_2$O$_3$, this work provides a systematic methodology for the unambiguous structural characterization of heterointerfaces involving materials with markedly different crystal symmetries.
