Strain-induced modifications of the electronic states of InGaAs quantum dots embedded in bowed airbridge structures

Abstract

We have fabricated bowed airbridges in which self-assembled InGaAs quantum dots are embedded. Strong strain distribution induced in the bowed airbridge and the effect on the electronic states of the quantum dots are investigated through the measurement of the photoluminescence from the individual dots and the theoretical calculation. A finite element calculation shows the strain in the bowed airbridge to distribute from tensile to compressive along the growth direction. The strain effect on the electronic states of the dots is probed through the photoluminescence peak shift following the deformation of the GaAs matrix of the dots from a wall-shaped structure to the bowed airbridge. The magnitude of the peak shift varies systematically with the position of the quantum dot along the growth direction, clearly reflecting the strain distribution in the bridge. The energy level shift following the deformation is calculated by solving the three-dimensional Schrödinger equation taking into account the strain distribution around the dots embedded in the bridge. The calculation, which agrees well with the experiment, demonstrates that the characteristic strain distribution around the dot embedded in the bowed airbridge modifies not only the energy levels, but also the wave functions. The electron and hole wave functions are modified differently, mainly due to the opposite contribution of the biaxial strain to the hydrostatic ones.