二维晶体材料上低缺陷密度氮化镓生长及物性研究

Recently, heteroepitaxy of GaN on two-dimensional (2D) materials gains great interest due to the various applications of both of flexible and transferable optoelectronic devices and distinctive heterojunction. It is a new approach known as quasi-van der Waals epitaxy. However, because of the lack of dangling bonds on the surface of 2D materials, the nucleation of GaN is limited. Therefore, the mechanism of this heteroepitaxy is different from the traditional heteroepitaxy, which needs to make a further investigation. The proposed project will study on heteroepitaxy of GaN on 2D materials, such as graphene, transition metal dichalcogenides, etc. Combined with first-principles calculation, by chemical treatment of the surface of 2D materials for promoting nucleation of GaN, we will study the mechanism of nucleation and growth of GaN on 2D materials systemically and establish the growth model of the quasi-van der Waals epitaxy. In addition, by regulation of the interface growth model, the project will also carry out an in-depth investigation of the growth kinetics model of defects, establish the mechanism of the formation, evolution and mitigation of defects, explore an effective way to obtain a low-dislocation-density GaN single crystal material, and develop mechanical release technology to obtain free-standing GaN single crystal substrate. Moreover, the project will make an explorative investigation of quantum structure, electrical transport, and photoelectric properties of the heterojunction of strongly polarized semiconductor and 2D materials.

二维晶体材料上外延生长氮化镓既可以获得易转移、柔性的光电器件，又可以构建形成独特的半导体异质结，成为近几年研究的热点，这种全新的外延方法被称为准范德瓦耳斯外延。然而，由于二维晶体材料表面缺乏悬挂键，限制了氮化镓在其上成核。因此，其外延生长机理与传统异质外延存在较大差异，有待于深入研究。本项目拟在石墨烯、过渡金属硫族化合物等二维晶体材料上开展氮化镓材料的外延生长研究。结合第一性原理计算，通过对二维晶体材料表面化学处理，促进氮化镓成核，系统研究二维晶体材料上氮化镓的成核及生长机理，建立准范德瓦耳斯外延的生长模型；进一步通过对界面生长模式的调控，深入研究缺陷生长动力学过程，建立缺陷形成及湮灭机制，掌握获得低缺陷密度氮化镓单晶材料的有效途径,开发氮化镓机械剥离技术，获得自支撑氮化镓单晶衬底。在此基础之上，开展强极化半导体与二维晶体材料异质结量子结构、电学输运及光电性质的探索性研究。

二维晶体材料上外延生长氮化镓既可以获得易转移、柔性的光电器件，又可以构建形成独特的半导体异质结，成为近几年研究的热点。本项目在石墨烯等二维晶体材料上开展了GaN材料的外延生长机理及其缺陷演化机理的研究。采用原位氨气氮化处理石墨烯表面，解决了石墨烯表面自由能小导致成核困难这一关键科学问题，在国际上首次揭示了范德瓦尔斯外延生长薄膜的生长模式是“layer by layer”的层状生长模式这一关键外延生长机理；通过采用具极性的基板增强石墨烯与外延层的界面作用力，解决了石墨烯上范德华外延存在大量晶界缺陷这一关键科学问题，在国际上创新性地提出了“远程轨道杂化”的概念，充分探讨了GaN和衬底之间的界面耦合特性。该工作受到了美国麻省理工学院“远程外延”概念提出者Kim在Nature Reviews Methods Primers期刊上的正面引用。.另外，发展了“自组装的石墨烯纳米掩膜”和“自消失的石墨烯掩膜”侧向外延技术，揭示了石墨烯上GaN缺陷起源及其演化机理，实现了位错密度10^6cm-2数量级的高质量GaN材料，并且机械剥离实现了2寸和4寸自支撑GaN单晶衬底。.在此基础之上，开展了二维晶体材料异质结量子结构的探索性研究，通过输运实验中观测的拓扑霍尔效应，在国际上首次验证了磁性斯格明子在拓扑绝缘体异质界面的存在，引起国内外课题组的广泛兴趣，已被引用达44次。