Influence of capping layer thickness on electronic states in self assembled MOVPE grown InAs quantum dots in GaAs

The influence of the capping layer on the structural and optical properties of InAs quantum dots grown on a GaAs substrate by metal-organic vapor phase epitaxy was investigated. The results show that the GaAs capping layer transforms originally elliptical lens like quantum dots into elongated structures or rhombus shaped objects with a central hole. This is accompanied by the blue shift of quantum dot luminescence maximum from 1.43 to 1.26 μm. Simulations of the electronic states in such quantum dot structures showed that this shift is caused both by the quantum dot shrinking and by the change of their band structure due to strain growth as the GaAs coverage increases. On the contrary In0.23Ga0.77As capping reduces the residual strain and preserves the shape of the quantum dots. As a result, the photoluminescence maximum shifts up to the desired wavelength of 1.55 μm.