Wang Xiaodan, Zhou Hua, Wilks Regan G, Hsieh Tzung-En, Yang Wanli, Zhang Yufeng, Zhan Huahan, Bai Lihui, Zheng Jin-Cheng, Bär Marcus, Kang Junyong, Wang Hui-Qiong
Engineering Research Center of Micro-nano Optoelectronic Materials and Devices, Ministry of Education, Fujian Key Laboratory of Semiconductor Materials and Applications, CI Center for OSED, and Department of Physics, Xiamen University, Xiamen 361005, China.
Department of Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 12489 Berlin, Germany.
ACS Omega. 2025 Jul 5;10(35):39639-39648. doi: 10.1021/acsomega.5c02932. eCollection 2025 Sep 9.
Nitrogen doping is a commonly employed and effective strategy to achieve p-type ZnO films. A detailed understanding of the ZnO film growth behavior resulting in epitaxy is essential for elucidating the doping mechanism. In this study, ZnO films are grown on nonpolar (101̅0) ZnO substrates using plasma-assisted molecular-beam epitaxy (PA-MBE). Introducing nitrogen during PA-MBE growth is expected to lead to the incorporation of N, thus affecting the film properties. Growth kinetics, surface morphology, and chemical structure of the films are thus investigated through reflection high-energy electron diffraction, scanning tunneling microscopy, and synchrotron-based X-ray absorption spectroscopy. Well-ordered "stripe-like" structures are observed on the surface of the N-free ZnO films that evolve into "corn-like" nanostructures upon nitrogen addition and further transform into a "particle-like" morphology as the N/O partial pressure ratio increases. Several nitrogen species, including N, NO, NO, and NO, are expected to exist during the growth process, with NO and NO molecules suggested to predominantly adsorb onto (101̅0) ZnO surfaces, where N-Zn bonds are likely to form. A pathway for this chemical structural change is proposed. This work aims to explore whether the supply of nitrogen during PA-MBE growth results in the incorporation of nitrogen into the ZnO lattice and whether this can be considered a doping mechanism. Hence, this work might contribute to a better understanding of nitrogen incorporation, potentially realizing (and deliberately optimizing the) p-type doping of ZnO films.
氮掺杂是实现p型ZnO薄膜常用且有效的策略。详细了解导致外延生长的ZnO薄膜生长行为对于阐明掺杂机制至关重要。在本研究中，使用等离子体辅助分子束外延（PA-MBE）在非极性（101̅0）ZnO衬底上生长ZnO薄膜。在PA-MBE生长过程中引入氮有望导致氮的掺入，从而影响薄膜性能。因此，通过反射高能电子衍射、扫描隧道显微镜和基于同步加速器的X射线吸收光谱研究了薄膜的生长动力学、表面形貌和化学结构。在无氮ZnO薄膜表面观察到有序的“条纹状”结构，在添加氮后演变成“玉米状”纳米结构，并随着N/O分压比增加进一步转变为“颗粒状”形貌。预计在生长过程中会存在几种氮物种，包括N、NO、NO和NO，其中NO和NO分子被认为主要吸附在（101̅0）ZnO表面，在那里可能形成N-Zn键。提出了这种化学结构变化的途径。这项工作旨在探索在PA-MBE生长过程中供应氮是否会导致氮掺入ZnO晶格，以及这是否可以被视为一种掺杂机制。因此，这项工作可能有助于更好地理解氮的掺入，潜在地实现（并有意优化）ZnO薄膜的p型掺杂。
