CIMAP, UMR 6252 CNRS, ENSICAEN, UCBN, CEA , 6 Boulevard du Maréchal Juin , 14050 Caen Cedex, France.
Key Laboratory of Materials Physics, Institute of Solid State Physics , Chinese Academy of Sciences , Hefei 230031 , China.
ACS Appl Mater Interfaces. 2018 Oct 31;10(43):37651-37660. doi: 10.1021/acsami.8b12202. Epub 2018 Oct 16.
In semiconductor heterojunction, polarity critically governs the physical properties, with an impact on electronic or optoelectronic devices through the presence of pyroelectric and piezoelectric fields at the active heteropolar interface. In the present work, the abrupt O-polar ZnO/Ga-polar GaN heterointerface was successfully achieved by using high O/Zn ratio flux during the ZnO nucleation growth. Atomic-resolution high-angle annular dark-field and bright-field transmission electron microscopy observation revealed that this polarity inversion confines within one monolayer by forming the (0001) plane inversion domain boundary (IDB) at the ZnO/GaN heterointerface. Through theoretical calculation and topology analysis, the geometry of this IDB was determined to possess an octahedral Ga atomic layer in the interface, with one O/N layer symmetrically bonded at the tetrahedral site. The computed electronic structure of all considered IDBs revealed a metallic character at the heterointerface. More interestingly, the presence of two-dimensional (2D) hole gas (2DHG) or 2D electron gas (2DEG) is uncovered by investigating the chemical bonding and charge transfer at the heterointerface. This work not only clarifies the polarity control and interfacial configuration of the O-polar ZnO/Ga-polar GaN heterojunction but, more importantly, also gives insight into their further application on heterojunction field-effect transistors as well as hybrid ZnO/GaN optoelectronic devices. Moreover, such polarity control at the monolayer scale might have practical implications for heterojunction devices based on other polar semiconductors.
在半导体异质结中，极性对物理性质起着至关重要的作用，通过在活性异质界面处存在热释电和压电场，对电子或光电设备产生影响。在本工作中，通过在 ZnO 形核生长过程中使用高 O/Zn 比通量，成功实现了 O 极性 ZnO/ Ga 极性 GaN 突变异质界面。原子分辨率高角度环形暗场和亮场透射电子显微镜观察表明，这种极性反转通过在 ZnO/GaN 异质界面处形成（0001）面反转畴界（IDB）限制在单层内。通过理论计算和拓扑分析，确定了该 IDB 的几何形状在界面处具有一个八面体 Ga 原子层，在四面体位置上对称地键合一个 O/N 层。所有考虑的 IDB 的计算电子结构在异质界面处呈现金属性质。更有趣的是，通过研究异质界面的化学结合和电荷转移，揭示了二维（2D）空穴气体（2DHG）或二维电子气体（2DEG）的存在。这项工作不仅阐明了 O 极性 ZnO/ Ga 极性 GaN 异质结的极性控制和界面结构，而且更重要的是，为异质结场效应晶体管以及混合 ZnO/GaN 光电设备的进一步应用提供了深入的了解。此外，在单层尺度上的这种极性控制可能对基于其他极性半导体的异质结器件具有实际意义。
