Picosecond Carrier Transport in GaAs Quantum Wells
Picosecond techniques, in conjunction with applied electric fields, provide valuable information about carrier transport phenomena of interest in ultrasmall, ultrafast semiconductor devices. We review here our recent measurements of minority carrier drift velocities in GaAs quantum wells which, in combination with luminescence measurements, provide information about high field phenomena such as real-space-transfer and electron-hole energy exchange. We also demonstrate that, under appropriate conditions, minority carriers in GaAs quantum wells exhibit negative absolute mobility i.e. the minority electrons drift towards the negative electrode and the minority holes drift towards the positive electrode. We show that this unusual phenomenon results from momentum scattering between electrons and holes and deduce a momentum relaxation time of ~ 80 fs for electrons in a hole plasma and ~ 4 ps for holes in an electron plasma.
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