The electronic structure of semiconductor nanocrystals

We review the rapid progress made in our understanding of the crystal properties of semiconductors and nanocrystals focussing on theoretical results obtained within the multiband effective mass approximation. A comparison with experiment shows these results are valid for nanocrystals down 22-26 Angstrom in diameter. The effect of the electron-hole Coulomb interaction on the optical spectra is analyzed. A theory of the quantum-size levels in wide gap (CdSe) and narrow gap semiconductors (InAs) is presented that describes the absorption spectra of these semiconductors well. A great enhancement of the electron-hole exchange interaction leads to the formation of the optically forbidden Dark Exciton in nanocrystals, which strongly affects their photoluminescence. A theory of the band-edge exciton fine structure is presented and applied to the study of the PL in CdSe nanocrystals. The effect of doping on nanocrystal spectra is considered. The enhancement of the short-range spin-spin interaction in Mn-doped nanocrystals leads to a giant splitting of the electron and hole spin sublevels.