摘要
We investigate the threading dislocation(TD)density in N-polar and Ga-polar GaN films grown on sapphire substrates by metal-organic chemical vapor deposition.X-ray diffraction results reveal that the proportion of screw type TDs in N-polar GaN is much larger and the proportion of edge type TDs is much smaller than that in Ga-polar.Transmission electron microscope results show that the interface between the AlN nucleation layer and the GaN layer in N-polar films is smoother than that in Ga-polar films,which suggests different growth modes of GaN.This observation explains the encountered difference in screw and edge TD density.A model is proposed to explain this phenomenon.
基金
Supported by the National Key Research and Development Program of China under Grant No 2016YFB0400100
the China Postdoctoral Science Foundation under Grant No 2015M582610