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A recent experiment on Stark effect spectroscopy in self-assembled quantum dots (SADs) has demonstrated the existence of an inverted electron-hole alignment due to the presence of gallium diffusion in InAs SADs and has established a relation between the Stark shift and the vertical electron-hole separation. The theoretical interpretation of these experimental results is based on the assumption that the applied electric field can be treated by the second-order perturbation theory, which results in a quadratical dependence of the transition energy on the applied electric field. While this relation is well satisfied in many quantum systems including single SADs and quantum well structures. But this relation is not valid for vertically coupled SAD structures, the asymmetric Stark shift of experimental measurement has shown existence of built-in dipole moment in InAs/GaAs QDs. Here we present a theoretical investigation of the factors influencing the sign and magnitude of the built-in dipole moment in realistic QD structures, including cubical, pyramidal and truncated pyramidal shape. The comparable results gave a reasonable interpretation for the experimental results.
Our calculations consist of two basic steps. First, the strain is calculated for particular dot geometry with Green function methods. Second, the single-electron states are calculated using an electronic Hamiltonian, which depends on the strain. The computed states can then be used to determine various quantities, such as optical transition strengths, or exciton binding energies. In the article, we use Green function for the strain calculation, and plane-waves expansion in the envelope function approximation for the electronic structure calculations. The theoretical results agree well with the available experimental data. Our calculated results are useful for the application of QDs to photoelectric devices.
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