Optical dephasing of light-hole excitons in GaAs single quantum wells

Picosecond photon-echo experiments were performed on light-hole excitons as well as heavy-hole excitons in GaAs single quantum wells at low temperatures and low excitation intensities. The absolute values of the exciton dephasing times depend on the sample quality but the ratio of the dephasing times of both exciton types reveals a strong increase in the dephasing rate of light-hole excitons when the thickness of the quantum well is reduced below 130 A. This enhanced dephasing of light-hole excitons is due to a Fano-type resonance when the lowest light- hole exciton state is energetically overlapping with electron-heavy-hole continuum states. The experimental results are in reasonable agreement with those of theoretical calculations.