DEPHASING TIMES IN MODULATION-DOPED QUANTUM-WELLS

Various single-particle and collective-mode scattering processes that contribute to the dephasing time of photoexcited electron-valence hole pairs in degenerate, modulation-doped quantum wells are discussed. Detailed calculations show that sharp structures in the energy dependence of the electron dephasing time can give information about short-range correlations associated with large-wavevector and high-frequency excitations of the coupled electron-LO phonon system. To extract dephasing times from coherent optical excitations the effects of the complex valence band structure, i.e. mixing of light and heavy holes in GaAs quantum wells, have to be taken into account. This is discussed in terms of the three-level semiconductor Bloch equations. Calculations are compared with recent experimental results by Kim et al.