Electron-Hole Drag in Semiconductors.

Transport of minority carriers in semiconductor plasmas can be strongly affected by electron-hole scattering. In high- mobility carrier systems not only the presence of one carrier type, but also its drift velocity determines the transport of the other carrier type via electron-hole scattering effect is known as "carrier drag". In modulation-doped quantum well structures the carrier drag is strong enough to cause "negative absolute mobility" of both minority electrons and holes. In this paper we describe all-optical transport measurements, from which momentum relaxation times by electron-hole scattering are quantitatively determined. Extremely short scattering times result for minority electrons in a hole plasma (40 to 100 fs) in contrast to the reverse case of holes in an electron plasma (2-5 ps).