Microstructural and optical properties of self-organized GaN quantum-dot assemblies

The microstructural and optical properties of GaN quantum-dot (QD) assemblies self-organized in two-dimensional GaN epilayers grown on Al _xGa _1-xN layers by using plasma-assisted molecular beam epitaxy were investigated with high-resolution scanning electron microscopy (HRSEM) and cathodoluminescence (CL) measurements. The HRSEM images showed that QD assemblies were formed in separate regions of the slightly stressed GaN epilayer on the Al _0.4Ga _0.6N surface and that the size and the density of the self-organized QD assemblies were affected significantly by the thickness and the surface polarity of the GaN layer. The CL spectra of the GaN QD assemblies showed a blue shift of the near band gap emission, and the position of the emission peak depended on the polarity and the thickness of the GaN epilayer. Deep level luminescence spectra indicated the existence of impurity-assisted QD assembly formation.