Terahertz electric polarizability of excitons in PbSe and CdSe quantum dots

Terahertz time-domain spectroscopy was employed to investigate photogenerated excitons in PbSe and CdSe quantum dots (QD) of radii less than their exciton Bohr radius. The exciton response was found to be atom-like and rise with increasing the carrier effective mass. Excitons in CdSe were found to be about two times more polarizable than those in PbSe QDs of equal size. These experimental findings including both the magnitude of the exciton polarizability and its variation with the QD radius were well described by an effective mass model with multiband structures of the QD materials.