Growth and optical investigation of self-assembled InGaN quantum dots on a GaN surface using a high temperature AlN buffer

InGaN quantum dots (QDs) with a high density up to $9×1010/cm2$ have been obtained on a surface of high quality GaN grown using high temperature AlN as a buffer layer on sapphire substrates. X-ray diffraction measurements indicate that the full width at half maximum of rocking curve of the GaN in (0002) direction has been reduced to as narrow as $61arcsec$⁠. The growth of the InGaN QDs has been found to be different from the formation of other III–V semiconductor QDs in the conventional Stranski–Krastanov mode. Too high $NH3$ flow rate leads to the InGaN QDs in a large diameter up to 50 nm with a density of $∼1010/cm2$⁠, while too low $NH3$ flow rate results in disappearance of the InGaN QDs. The growth mechanism for the InGaN QDs due to the change in $NH3$ flow rate has been discussed. The optical properties of the InGaN QDs have been investigated. A stimulated emission from the InGaN multiple QD layers has been observed under an optical pumping with a low threshold at room temperature. The influence of thickness of the GaN barrier and growth temperature for the GaN barrier on InGaN QDs has been investigated, in combination with optical pumping measurements. Our results indicate that both the thickness of the GaN barrier and growth temperature for the GaN barrier should be carefully chosen. Otherwise, either the formation of the InGaN QDs can be prevented or the InGaN QDs that have been formed can be destroyed.