面向氮化物光电器件的石墨烯透明导电空穴注入层生长，掺杂和耦合机制研究

The graphene based transparent conductive hole injection layer is proposed, which is aimed at nitride based optoelectronic devices, including the research on growth, doping and coupling mechanisms. The first-principle and molecular dynamics calculation is adopted to simulate the inter-diffusion and distribution behavior of carbon on nitride materials, and to break the bottleneck of direct CVD growth on nitride device epilayer. The proposed graphene based transparent conductive hole injection layer is a promising candidate to replace traditional indium tin oxide and p-type GaN in nitride based optoelectronic devices.This novel graphene based structure has the advantage of getting rid of the damage caused by typical chemical etching and transfer processes, which is a vital part in state-of-art graphene transfer process. Systematic investigations are performed on the optimization of parameters in CVD growth of graphene on nitride, which are of importance to the crystal quality of graphene. Moreover, the formation mechanism of graphene on nitride is studied both theoretically and experimentally. Then, in order to obtain a high and controllable hole density, the modification of work function of graphene is analysed by chemical doping.The influences of various doping species on the transmissivity and conductivity of graphene are intensively studied, a trade off is necessary to optimize the performance of graphene layer. These could minimize the band offset between graphene and nitride, leading to effective hole injection to nitride based active region. Additionally, the coupling between graphene film and nitride epilayer is also a key factor to hole transportation, which is also a focal point in this proposal.

本项目面向氮化物光电器件提出基于石墨烯薄膜结构的透明导电空穴注入层概念，研究其生长，掺杂和耦合机制。首先，采用第一性原理和分子动力学模拟碳元素在氮化物材料表面的互扩散和分布行为，突破在氮化物外延层上直接使用化学气相沉积（CVD）生长石墨烯的技术难题，以替代传统氮化物光电器件中的ITO透明电极和p型氮化物空穴注入层的功能。力求从物理本质上摒弃在金属衬底制备的石墨烯向半导体材料的传统转移过程和转移损伤。系统的研究CVD生长参数对石墨烯晶体质量的影响，深入理解石墨烯在氮化物表面的成膜机制。其次，通过化学掺杂调整石墨烯功函数，提高p型掺杂的空穴浓度，降低石墨烯和氮化物半导体材料之间的接触势垒，在石墨烯的透过率和电导率之间寻找最佳平衡点，以优化氮化物光电器件的性能。最后，通过理论和实验手段分析石墨烯空穴注入层与氮化物器件外延层之间的耦合方式，实现空穴从石墨烯薄膜向氮化物有源区的注入。