石墨烯/氮化镓半导体异质结界面态及其对载流子输运的影响研究

Due to its superior physical and chemical properties and ease of manipulation, graphene offers the great potentialities of integration with the existing semiconductor technology for novel electronic and opto-electronic devices. Lots of research shows that the uncertainty and uncontrollability of the interfacial properties between graphene and nitride semiconductors are the most obstacles to fabricate the desirable integrated devices. As for its essence, electron and hole movement mechanisms, which are determined by the interfacial states, are still unclear. But so far, the mico-morphology and formation of the interfacial states in graphene-semiconductor are the lack of thorough understanding. The real morphology of interfacial states affected by multiple factors in atomic world will be revealed using a direct measurement on the atomic scale. In this project, we take the interface between graphene and gallium nitride (GaN) as a typical object of study, which is influenced by the relative rotation angle between the graphene and GaN crystals, doping concentration and crystal faces of GaN crystals. In the ultra-high-vacuum conditions, we propose to investigate the overlapping states of the electronic wave function with the scanning tunneling microscopy. The types and energy band structures of interfacial states can be acquired by the analysis of moiré pattern and scanning tunneling spectroscopy. And then, the carrier transport and photogenerated carrier recombination processes at the different interfacial states can also be obtained measured by conductive atomic force microscopy and photo-assisted kelvin probe microscopy. Furthermore, we will explore the possibility of the artificial regulation of interface electrical and optical properties by the high resolution measurement of the interfacial states at nano-scale. The study will benefit the approach to optimal designing of graphene- semiconductor devices.

石墨烯因其优良的理化性质和易于加工等特点，与氮化物半导体技术集成可构建新颖的电子和光电器件。目前制约器件性能的主要障碍是石墨烯-半导体界面接触的不确定和不可控性。界面特性的本质是电子空穴在界面中的跃迁、输运和复合过程，界面态是决定这些过程的关键。但是对于石墨烯-氮化物半导体界面态的微观形态和调控方法仍缺乏深入理解。因此有必要在原子尺度对界面态进行直接测量，揭示界面态的来源及其对载流子输运的作用机制。本项目以石墨烯-氮化镓半导体界面为研究对象，通过调节二者晶向夹角、氮化镓不同晶面和掺杂浓度，利用超高真空扫描隧道显微镜在原子级别上表征电子波函数交叠状态，通过分析摩尔条纹和扫描隧道谱确定界面态的类型和能带结构，原位应用导电原子力和光辅助开尔文探针显微镜研究不同界面态下的载流子输运机制以及光生载流子复合过程，探索通过原子级分辨的界面态测量，实现界面电学和光电特性的人工调控，为优化器件设计奠定基础。

本项目在实施过程中，发展出了一整套切实可行的、可应用于超高真空STM研究的样品制备方法，包括石墨烯的PPC转移方法，石墨烯/GaN界面二者晶面夹角可控制备方法，并首次全面、深入地研究了HVPE生长c面（极性面）、a面和m面（非极性面）、及r面（半极性面）GaN表面结构的化学腐蚀特性，及其在原子力显微镜（AFM）表征上的独特结构特征。基于扫描探针显微镜技术，首次创新性的发展了一个Kelvin探针力显微镜（KPFM）结合导电原子力显微镜（C-AFM）测量半导体表面石墨烯载流子局域迁移率的方法，通过该方法研究了受GaN衬底影响的石墨烯的载流子输运性质，揭示了解理石墨烯、CVD生长石墨烯分别与GaN形成异质结后，不同GaN掺杂类型、界面能带结构、GaN载流子浓度和表面结构等因素对石墨烯载流子输运性质的影响。通过自主研发的超高真空STM高分辨测量研究，发现相对于纯石墨烯，不同石墨烯/GaN晶向夹角样品，由其表面原子电子态密度分布构成的摩尔条纹将出现差异，说明二者晶向夹角将影响石墨烯和GaN在界面处电子波函数的交叠状态。