(n11)GaAs衬底上高质量Ga(In)AsN的外延生长及光伏性能研究

III-V-N dilute nitride [Ga(In)AsN] attracts intense research interest as the promising material to fulfill the energy-gap requirement of three-/four-junction solar cells while keeping lattice-matched to GaAs. However, various electrically active defects due to the quite low solubility of N in Ga(In)As lead to the dramatic decrease in the minority-carrier diffusion length, which hinders its effective applications in multijunction solar cells. In this proposal, a novel method to construct active absorption sites for N adatoms is raised by engineering the epitaxial orientation. Key scientific issues, including efficient incorporation of N into the substitutional site and suppressing the formation of N related defects that deteriorate the optical and electrical properties of Ga(In)AsN, will be solved. Through constructing models of the atomic bonding geometry and growth kinetics, the growth orientation dependent N incorporation mechanism, the role of In on N incorporation, N-related defect generation mechanism, and the doping mechanisms of typical II/IV/VI element dopants will be clarified. Technologies for cell device fabrication and film epitaxy of Ga(In)AsN with target bandgap and high photovoltaic performance will be developed. This project aims to provide the material basis for realizing practical applications of Ga(In)AsN in high-efficiency multijunction solar cells.

Ga(In)AsN由于能与GaAs晶格匹配，并满足高效三结或四结太阳能电池的带隙要求而备受瞩目。但N在Ga(In)As中均匀并入困难，由此产生的N缺陷降低了少数载流子的扩散长度，严重限制了该材料体系在多结太阳能电池中的应用。因而研究Ga(In)AsN材料中N的并入行为、电活性缺陷的产生机制和控制方法具有重要意义。本项目提出通过改变Ga(In)AsN材料的外延取向，在生长表面构筑N的活性吸附位的方法，拟解决Ga(In)AsN材料中N在替位的高效并入及抑制导致光电性能劣化的N缺陷的产生等关键科学问题。通过建立表面原子结构模型及生长动力学模型，揭示在不同外延取向下N的并入机制、In对N并入的影响机制、N缺陷的产生机制、及典型II、IV、VI族元素的掺杂机制；提出目标带隙下光伏性能优异的Ga(In)AsN的薄膜外延方法及电池器件工艺；为Ga(In)AsN材料在高效多结太阳能电池中的应用奠定基础。

Ga(In)AsN相关材料因为在满足多结太阳能电池带隙要求的同时能够与GaAs或Ge晶格匹配而备受关注。本项目提出了一种利用改变GaAs衬底取向来提高N在GaAs中有效并入、降低N间隙缺陷产生的外延生长方法，拟解决高质量Ga(In)AsN材料外延生长过程中的关键问题。思路上，提出利用(n11)B极性面（即As面）形成高密度三键V位（即N或As位），并结合N的高电负性特性来构筑N的活性吸附位；实验上，重点发展了不同衬底取向下Ga(In)AsN材料的外延生长技术及物性分析测试手段，对重要电池器件工艺进行了优化设计；理论上，建立了(n11)面GaAsN外延生长的原子构造模型，通过第一性原理计算分析了缺陷态的形成机制和控制机制。在此基础之上，掌握了获得掺杂可控、光电性能优异的Ga(In)AsN薄膜外延生长技术，为Ga(In)AsN材料体系在高效多结太阳能电池中的应用奠定基础。