TIME-RESOLVED OPTICAL INVESTIGATIONS OF BLOCH OSCILLATIONS IN SEMICONDUCTOR SUPERLATTICES

We present a complementary study of the interband and intraband dynami cs of optically excited Bloch oscillations in GaAs/AlxGa1-xAs superlat tices. Distinct differences in the frequency and dephasing of the osci llations give evidence for Bloch oscillations performed by electrons i n continuum states and by excitonic wavepackets. The dephasing time of the electronic continuum states is found to be exceptionally long as compared to the excitonic dephasing time under identical excitation co nditions. These observations are confirmed by THz emission experiments , where Bloch oscillations are detected under optical excitation well above the fundamental band gap. The experimental observations suggest that the electronic coherence may be partially maintained during relax ation and momentum scattering processes.