EFFECT OF CONFINEMENT ON ENERGY-DEPENDENT DEPHASING IN HETEROSTRUCTURES

To study the effects of confinement by quantum-well potential disconti nuities on excitonic dephasing, we performed a spectrally and temporal ly resolved study of band-edge four wave mixing emission from a series of In1-xGaxAs quantum wells. Our measurements reveal an array of dyna mics as we move from the three-dimensional to the two-dimensional limi t. Spectral resolution allows us to resolve a slowly dephasing exciton ic contribution in bulk In1-xGaxAs. In measurements on quantum-well sa mples of intermediate width, we find no change of the dephasing time a s the quantum-well width becomes smaller than the bulk Bohr diameter. This indicates that the dominant dephasing mechanism in this regime is scattering by alloy disorder and interface roughness. For quantum-wel l widths below 200 Angstrom we observe a substantial increase of the d ephasing time. Spectral resolution allows us to associate the slow dep hasing in this regime with localized excitons.