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Atomistic electronic structure calculations are performed to study thecoherent inter-dot couplings of the electronic states in a single InGaAsquantum dot molecule. The experimentally observed excitonic spectrum [12] isquantitatively reproduced, and the correct energy states are identified basedon a previously validated atomistic tight binding model. The extended devicesare represented explicitly in space with 15 million atom structures. An excitedstate spectroscopy technique is presented in which the externally appliedelectric field is swept to probe the ladder of the electronic energy levels(electron or hole) of one quantum dot through anti-crossings with the energylevels of the other quantum dot in a two quantum dot molecule. This techniquecan be applied to estimate the spatial electron-hole spacing inside the quantumdot molecule as well as to reverse engineer quantum dot geometry parameterssuch as the quantum dot separation. Crystal deformation induced piezoelectriceffects have been discussed in the literature as minor perturbations liftingdegeneracies of the electron excited (P and D) states, thus affectingpolarization alignment of wave function lobes for III-V Heterostructures suchas single InAs/GaAs quantum dots. In contrast this work demonstrates thecrucial importance of piezoelectricity to resolve the symmetries and energiesof the excited states through matching the experimentally measured spectrum inan InGaAs quantum dot molecule under the influence of an electric field. Bothlinear and quadratic piezoelectric effects are studied for the first time for aquantum dot molecule and demonstrated to be indeed important. The netpiezoelectric contribution is found to be critical in determining the correctenergy spectrum, which is in contrast to recent studies reporting vanishing netpiezoelectric contributions.

Quantitative Excited State Spectroscopy of a Single InGaAs Quantum Dot Molecule through Multi-million Atom Electronic Structure Calculations