GaN表面区杂质和缺陷形成、离化及扩散行为的研究

The core of the semiconductor lighting technology is the GaN-based materials. Experimentally, it was found that formation, ionization and diffusion behaviours of defects and impurities located in GaN surface area are significantly different from the case of bulk GaN. Due to the current theoretical work mainly focus on the defects and impurities physics research in bulk GaN, people do not have a clear understanding of the defects and impurities physics in GaN surface till now.So, based on our previous studies of doping mechanism in bulk GaN, this project mainly focuses on physical behaviours of defects and impurities in GaN surface. The different GaN surface orientation would be considered, including polar, nonpolar and semipolar surface. Several methods in computational materials science would be used to calculate the formation energies, ionization energies, diffusion energy barriers and diffusion paths of defects and impurities in GaN surface area. Both spatial distribution and stability of defects and impurities under the surface potential would be discussed in detail. Aslo,the influence of surface orientation and stress on defects and impurities physical behaviours would be analysed, respcectively. Lastly, the electronic structure of surface system would be studied, in order to establish a relationship between the physical behaviors of defects and impurities and surface potential. Therefore, the research might provide theoretical support and guidance for synthesizing high quality GaN-based materials.

GaN基材料是半导体照明技术的核心。实验发现GaN表面区域中的缺陷和杂质的形成、离化及扩散行为呈现出与体中明显不同的情形，由于现有工作主要集中于块体中的缺陷和杂质物理研究，目前对它们在表面区中的这些物理行为的理解还很不清晰。为此，本项目拟在前期GaN块体掺杂机制的研究基础上，以GaN表面区本征点缺陷和杂质为研究对象，系统研究表面作用下的缺陷和杂质形成、离化及其扩散等相关科学问题。我们采用计算材料学方法计算缺陷和杂质在GaN表面区不同空间位置的形成能，探讨它们在表面势场的作用下而呈现出的空间分布规律；计算缺陷和杂质的扩散势垒及扩散路径，探讨它们在GaN表面区的稳定性规律；计算缺陷和杂质在GaN表面区不同空间位置的离化能；探讨缺陷和杂质行为对表面取向和应力作用的敏感。通过分析电子结构，建立表面区域中杂质和缺陷上述物理行为与GaN表面的关系，为实验上实现高质量GaN基薄膜材料提供理论支持和指导。

氮化镓(GaN)具有优异的光电性能，在光电子器件尤其是发光二极管(LED)方面具有巨大的应用价值。高质量GaN基材料和低阻GaN欧姆接触的设计和制备是决定LED器件性能的关键问题。.课题组选取多个具有代表性的低维GaN掺杂体系开展研究，紧密结合实验现象，系统研究了杂质形成能、离化能、掺杂体系的几何结构及电子结构，揭示了杂质和缺陷对GaN电学性质等物性的影响机制。主要结果如下：（1）阐明了Al在clean GaN(0001)和Ga-bilayer GaN(0001)的形成、扩散和分布等物理行为，解释了实验上富N条件下形成一种高度规则超晶格结构的现象，进而揭示了AlGaN薄膜材料生长机理。（2）阐明了Co在GaN表面的吸附行为，发现了Co掺杂表面体系的磁性特征与生长环境及表面形貌相关，且其铁磁性的稳定存在与紧密结合的CoGa bilayer结构直接关联。解释了Co在GaN(0001)表面上基于生长氛围的磁性机制，并提出了磁性调制思路。（3）阐述了Ag合金提高GaN欧姆接触稳定性机理，解释了Ag吸附性下降、出现集聚并导致器件性能显著下降的实验现象，提出采用AgNi合金有望改善GaN欧姆接触热稳定性的实验设计思路和方案。（4）揭示了本征缺陷、非磁性元素（Si/Mg）和过渡金属Mn掺杂ML-GaN体系的电子结构和磁性机理，发现应力能够调制Mn掺杂ML-GaN磁性且铁磁反铁磁转变临界点为-9.5%应力。（5）研究表明Ni及其诱导的Ga空位可在不同程度上降低p型Ag/GaN界面肖特基势垒高度，解释了实验发现的牺牲Ni退火技术可提高p型欧姆接触性能的现象。（6）计算获得了单层GaN的本征热导率仅为14.93W/mK，电子结构分析表明特殊的sp轨道杂化、强极性Ga-N键、非均匀分布的电荷密度导致了单层GaN具有较大的声子非简谐性，进而导致低的本征热导率。.在Scripta Mate., J. Appl. Phys.,J. Phys. Chem. Solids和Appl.Surf. Sci. 等刊物发表SCI&EI论文14篇，授权专利5件，申请专利2件，培养硕士研究生7名。研究成果无论是对于深化GaN基LED器件和物理的认识上，还是实际应用上均有重要的科学意义和应用价值，将有力促进南昌光谷的健康持续发展。