Density Increase of Upper Quantum Dots in Dual InGaN Quantum-Dot Layers

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 1.3×10^(9) 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 2.6×10^(10) cm^(−2),4.6 nm and 81.3 nm,respectively.Two reasons are proposed to explain the QD density increase in the upper layer.First,the strain accumulation in the upper layer is higher,leading to a stronger three-dimensional growth.Second,the GaN barrier beneath the upper layer is so rough it induces growth QDs.