Giant permanent dipole moments of excitons in semiconductor nanostructures

We report measurements of the vertical permanent dipole moment and the polarizability of excited quantum rings by using single-dot spectroscopy. The rings are self-assembled using a modified Stranski-Krastanow growth procedure. The permanent dipole moment is surprisingly large, corresponding to electron-hole separations comparable to the quantum rings' vertical height, and opposite in sign to that of more conventional InAs quantum dots. The polarizabilities are consistent with vertical confinement lengths of about 3 nm for both electrons and holes, We find large fluctuations in both the excitonic dipole moment and polarizability from ring to ring, but a linear relationship between these two quantities. (C) 2002 Elsevier Science B,V. All rights reserved.