Ultrafast spin-polarized electrical currents injected in a strained zinc blende semiconductor by single color pulses

Ultrafast ballistic electrical currents are generated through interband excitation of strained InGaAs / GaAs quantum well samples at 295 K by 8 10 run, 60 fs circularly polarized optical pulses. These currents are generated through quantum interference of optical absorption pathways associated with the orthogonally polarized components of the light field, and although the spin of the currents is not directly measured, they should also be spin polarized. The femtosecond transient currents are detected via the emitted tetrahertz (THz) radiation which has a bandwidth of similar to8 THz. The THz amplitude scales linearly with injected carrier density up to similar to10(18) cm(-3) beyond which state filling and carrier-carrier scattering cause a sublinear dependence. A peak current density of 9 kA/cm(2) is obtained for a peak pump intensity of 250 MW/cm(2). (C) 2005 American Institute Of Physics.