Effect of the lifting of Kramer's degeneracy on excitonic linewidths in quantum well optical modulators

In symmetric quantum well structures, the hole subband states maintain the spin degeneracy (Kramer’s degeneracy), but in asymmetric quantum wells and in optical modulators in the presence of electric field, the degeneracy is lifted. This results in splitting of excitonic transitions due to splitting in the exciton binding energy. For small splitting this will result in exciton broadening. Comparisons are presented for this broadening in symmetric and asymmetric quantum well structures as a function of electric field. The light hole exciton is found to broaden at an order of magnitude higher rate than the heavy hole exciton. Field-dependent experimental results for symmetric GaAs/Al0.3Ga0.7As multiquantum well structures are carried out and support the theoretical results.