Yellow-Green Luminescence Due to Polarity-Dependent Incorporation of Carbon Impurities in Self-Assembled GaN Microdisk
Zhiwei Si, Zongliang Liu, Yaoqiao Hu, Xiaoxuan Wang, Chunxiang Xu, Shunan Zheng, Xiaoming Dong, Xiaodong Gao, Jingjing Chen, Jianfeng Wang, Ke Xu
Abstract
Yellow-green luminescence (YGL) competes with near-bandgap emission (NBE) for carrier recombination channels, thereby reducing device efficiency; yet uncovering the origin of YGL remains a major challenge. In this paper, nearly stress-free and low dislocation density self-assembled GaN microdisks were synthesized by Na-flux method. The YGL of GaN microdisks highly depend on their polar facets. Variable accelerating voltage/power CL, variable temperature PL, and Raman spectroscopy are further performed to clarify the origin of polarity dependence of GaN microdisk YGL behavior, which indicates its independence of dislocations, surface effects, stress, crystalline quality, and gallium vacancies. It was found that the incorporation ability of carbon impurities in the polar (0001) facet is greater than that in the semipolar (101̅1) facets, producing higher content of CN or CNON defects, resulting in a more pronounced YGL in the polar (0001) facet of GaN.