Optical performance improvement of GaN/AlN quantum dots via a two-step grown caplayer

A two-step growth technique consisting of a low temperature pulsed atomic layer epitaxy (PALE) method and high temperature PALE method has been employed to deposit the AlN caplayer over GaN quantum dots (QDs). The results show that the photoluminescence intensity of GaN QDs with this two-step grown caplayer has been overall enhanced significantly and most enhancement occurs at the lower energy side compared with that of the GaN QDs with low temperature one-step grown AlN caplayer, which is mainly due to the decreased defects of the AlN caplayer and the preferential wetting layer carrier transportation to larger QDs. - Highlights: • GaN quantum dots were grown on AlN by MOCVD in S–K mode. • The capping process was investigated to improve PL properties. • Two-step capping process has enhanced the PL intensity significantly. • Most enhancement occurs at the lower energy side of PL spectra. • The carriers in the Wetting layer preferentially transport to the large QDs.