Electronic structure and energy relaxation in strained InAs/GaAs quantum pyramids

Abstract

We perform experimental and theoretical studies of the electronic structure and relaxation processes in pyramid shaped InAs/GaAs quantum dots (QDs), grown by molecular beam epitaxy in the Stranski-Krastanow growth mode. Structural properties are characterized with plan view and cross section transmission electron microscopy. Finite difference calculations of the strain and the 3D Schrödinger equation, taking into account piezoelectric and excitonic effects, agree with experimental results on transition energies of ground and excited states, revealed in luminescence and absorption spectra. We find as relative standard deviation of the size fluctuation ξ=0.04; the pyramid shape fluctuates between {101} and {203} side facets. Carrier capture into the QD ground state after carrier excitation above barrier is a very efficient process. No luminescence from excited states is observed at low excitation density. Energy relaxation processes in the zero-dimensional energy states are found to be dominated by phonon energy selection rules. However, multi-phonon emission (involving GaAs barrier, InAs wetting layer, InAs QD and interface modes) allows for a large variety of relaxation channels and thus a phonon bottleneck effect does not exist here.