Semiconductor Quantum Dots

The “Standard Model” of the Electronic Structure of Dots Progress made in the growth of “freestanding” (e.g., colloidal) quantum dotslt2 (see also articles in this issue by Nozik and MiCi6, and by Alivisatos) and in the growth of semiconductor-embedded (“self-assembled”) dots3p4 (see also the article by Bimberg, Grundmann, and Ledentsov in this issue) has opened the door to new and exciting spectroscopic studies of quantum structures. These have revealed rich and sometimes unexpected features such as quantum-dot shapedependent transitions, size-dependent (red) shifts between absorption and emission, emission from high excited levels, surface-mediated transitions, exchange splitting, strain-induced splitting, and Coulomb-blockade transitions. These new observations have created the need for developing appropriate theoretical tools capable of analyzing the electronic structure of 103-106-atom objects. The main challenge is to understand (a) the way the one-e/e&on levels of the dot reflect quantum size, quantum shape, interfacial strain, and surface effects and (b) the nature of “many-particle” interactions such as electron-hole exchange (underlying the “red shift”), electronhole Coulomb effects (underlying excitonic transitions), and electron-electron Coulomb (underlying Coulomb-blockade effects). Interestingly, while the electronicstructure theory of periodic solids has been characterized since its inception by a diversity of approaches (all-electron versus pseudopotentials; Hartree Fock versus density-functional; computational schemes creating a rich “alphabetic soup,” such as APW, LAPW, LMTO, KKR, OPW, LCAO, LCGO, plane waves,