Abstract

We have used two-beam self-diffraction (photon-echo) techniques to directly measure and study the dephasing of both free excitons and free carriers optically excited in a series of multiple quantum well (MQW) structures as a function of sample geometry (well and barrier width), temperature and exciton or carrier density. These studies allow the separation of the various contributions to the dephasing. Specifically, they permit a measurement of the temperature-dependence of the dephasing associated with the acoustic and polar optical phonons and a determination of the density-dependence of the dephasing arising from carriercarrier and impurity scattering. Moreover, we observe quantum beating between light- and heavy-hole excitons in the dephasing data and study the variation of the beat frequency and amplitude as a function of sample geometry, temperature, excitation wavelength and fluence.

© 1992 IQEC