Photoluminescence Properties of GaN Nanowires Grown in a Gradient-Plasma Environment

Herein, we report the plasma effect on the surface defects of GaN nanowires (NWs). A gradient plasma growth system by microwave plasma chemical vapor deposition is demonstrated for NWs growth. The structure and surface defects of NWs are affected by the plasma distribution. The PL results show that emission peaks at ∼355, ∼374, and ∼389 nm arising from near band edge emission are observed from the GaN NWs under different plasma growth environment. The relative emission area (E_relative) of the specific emission peaks to total emission area (E_total) from the different growth regions also changes. The reason for variant ratio E_relative/E_total is related to the surface defects including structural defects and oxygen incorporation according to the results of high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The analysis of PL properties provided a strong evidence for formation of distinct surface defects. The emission mechanism of GaN NWs grown in a high-density plasma environment enriches our understanding of the plasma effects on the surface defects and optical property, and the knowledge is important to the development of nano-optoelectronic devices.