Self-assembled structures of closely stacked InAs islands grown on GaAs by molecular beam epitaxy

Closely stacked Stranski-Krastanow (S-K) growth islands were investigated. InAs islands of nominal 1.8 monolayer thickness were grown periodically with GaAs intermediate layers of less then 3 nm by molecular beam epitaxy. Reflection high-energy electron diffraction and atomic force microscopy revealed that S-K growth islands were formed even with stacked intervals of 2 nm, but the upper island size expanded slightly as the number of stacked layers increased. Transmission electron microscopy revealed that upper islands grew closely just on the lower islands aligning vertically on the first layer islands. Drastic decrease in photoluminescence full-width at half-maximum less than 30 meV was obtained from this structure.