Optical properties of InAs quantum dots with InAlAs∕InGaAs composite matrix

InAs quantum dots (QDs) in various matrices, such as InAlAs, InGaAs, InAlAs∕InGaAs, and InGaAs∕InAlAs, are prepared to clarify how the overgrown layers affect their optical properties. It is shown that strain reduction mechanism dominates the emission wavelength extension when the thickness of the overgrown layer is thin. The relaxation of compressive strain at the QD bottom by InAlAs overgrown layer cannot only extend the QD emission wavelength but also narrow the spectral linewidth and increase the state separation between the ground state and the first excited state.