Effect of confinement on energy-dependent dephasing in heterostructures

To study the effects of confinement by quantum-well potential discontinuities on excitonic dephasing, we performed a spectrally and temporally resolved study of band-edge four wave mixing emission from a series of (Formula presented)(Formula presented)As quantum wells. Our measurements reveal an array of dynamics as we move from the three-dimensional to the two-dimensional limit. Spectral resolution allows us to resolve a slowly dephasing excitonic contribution in bulk (Formula presented)(Formula presented)As. In measurements on quantum-well samples of intermediate width, we find no change of the dephasing time as 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-well widths below 200 Å we observe a substantial increase of the dephasing time. Spectral resolution allows us to associate the slow dephasing in this regime with localized excitons.