Single and dual layers of InGaN quantum dots(QDs)are grown by metal organic chemical vapor deposition.In the former,the density,average height and diameter of QDs are 1.3 × 109 cm-2,0.93 nm and 65.1 nm,respectively.The latter is grown under the same conditions and possesses a 20 nm low-temperature grown GaN barrier between two layers.The density,average height and diameter of QDs in the upper layer are 2.6 × 1010 cm-2,4.6nm and 81.3nm,respectively.Two reasons are proposed to explain the QD density increase in the upper layer.First,the strain accumulation in the upper layeris higher,leading to a stronger three-dimensional growth.Second,the GaN barrier beneath the upper layer is so rough it induces growth QDs.