For spatially and temporally localized laser excitation of a semiconductor quantum well qualitatively different behavior is predicted assuming resonant exciton or interband excitation conditions. Whereas the dynamic evolution of an excitonic distribution always consists of a spatial broadening, optical excitation above the band edge creates electron-hole wave packets that propagate pulselike through the medium.

• Received 7 March 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.550