Spiral growth of InGaN/InGaN quantum wells due to Si doping in the barrier layers

We have examined Si-doping effects in InGaN/InGaN quantum-well (QW) structures, especially the influence of Si-doped InGaN barrier layers on the growth mechanism of QW structures, by atomic force microscopy (AFM) and by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. Our AFM observations revealed that Si-doped InGaN barriers strongly affect the growth mode of overlying InGaN QW layers. This effect leads to the formation of nanoscale islands (with a density of 108 cm−2) due to spiral growth of the QW layers. The spirally grown nanoscale islands significantly increase the PL intensity. Through spatially resolved CL observations, we found that the number of dot-like CL bright spots increased dramatically when the barrier layers were Si doped, and the increased density of the spots was in good agreement with the increased density of the nanoscale islands observed by AFM. By combining these results, we show that the spirally grown QW structures produced by Si doping of the barriers effectively reduce the fluctuation of the band-gap potential in InGaN QW layers.