Electronic structure, impurity binding energies, absorption spectra of InAs/GaAs quantum dots

The influence of structural size and geometry on the electronic energy levels, impurity binding energies, and absorption characteristics of InAs/GaAs quantum dots grown in the Stranski-Krastanow mode is investigated. Our calculation accounts for the variation in the strain throughout these structures using the valence force field method. A multiband effective mass approach to describing the dot states has been adopted. We predict a strong absorption response in the 1.0-1.1 eV range of energies, in agreement with several recent experiments. Furthermore, the optical spectra are dominated by features arising from transitions between states with the same quantum numbers and transitions between states whose quantum numbers differ by one. Whether a dot exhibits a near-band gap absorption response due to transitions of the latter type depends on the aspect ratio of its base radius and height in a way that can be predicted from a simple particle in a rigid rectangular box model. We have also found that the pyramidal geometry of the dot plays an important role in determining the binding energy of a donor impurity placed at different positions within the dot. (C) 1998 Elsevier Science B.V. All rights reserved.