Size-tunable exchange interaction in InAs/GaAs quantum dots

Single epitaxial quantum dots are promising candidates for the realization of quantum information schemes due to their atom-like electronic properties and the ease of integration into optoelectronic devices. Prerequisite for realistic applications is the ability to control the excitonic energies of the dot. A major step in this direction was recently reached by advanced self-organized quantum-dot growth, yielding ensembles of equally shaped InAs/GaAs dots with a multimodal size distribution. The well-defined sizes of spectrally well separated subensembles enable a direct correlation of structural and excitonic properties, representing an ideal model system to unravel the complex interplay of Coulomb interaction and the quantum dot's confining potential that depends on size, shape, and composition. In this paper we focus on the exciton-biexciton system with emphasis on the excitonic fine-structure splitting. Across the whole range of size variations within our multimodal quantum dot distribution a systematic trend from +520 mu eV to -80 mu eV is found for decreasing dot size. To identify the underlying effects calculations of the fine-structure splitting are performed. A systematic variation of the structural and piezoelectric properties of the modeled quantum clots excludes shape anisotropy and tags piezoelectricity as a key parameter controlling the fine-structure splitting in our quantum dots.