This paper reported a structural and optical study of single InN/GaN dots with varying GaN cap thickness. The surface morphology of the 10-nm thick GaN capping layer shows a truncated pyramidal shape and changed to a dome shape when the thickness of the capping layer increases to 20-nm. The increase in compressive strain of InN dots with the increase in the cap thickness was analyzed by high resolution x-ray diffraction (HRXRD). A redshift was observed in the photoluminescence (PL) peak energy of the InN dots with increasing GaN capping thickness. The redshift of the PL peak energy of the 20-nm thick GaN capping layer sample was believed to be due to the GaN capping avoids InN decomposition and decreases the surface defect density. In addition, the maximum PL intensity of the 20-nm thick GaN capping layer sample was similar to 2.5 times higher than that of the uncapped sample. (C) 2011 Elsevier B.V. All rights reserved.