Ratchet effects induced by terahertz radiation in heterostructures with a lateral periodic potential

We report on the observation of terahertz radiation induced photogalvanic currents in semiconductor heterostructures with one-dimensional lateral periodic potential. The potential is produced by etching a grating into the sample surface. The electric current response is well described by phenomenological theory including both the circular and linear photogalvanic effects. Experimental data demonstrate that the inversion asymmetry of the periodic lateral pattern can be varied by means of electron beam lithography to produce classical lateral ratchets. A novel microscopical mechanism for the polarization-dependent photogalvanic effects has been proposed to interpret the experimental findings. The photocurrent generation is based on the combined action of the lateral periodic potential and the modulated in-plane pumping. The latter modulation stems from near-field effects of the radiation propagating through the grating.Comment: 8 pages, 6 figure

Spiranthes vernalis Engelm. & A. Gray

https://thekeep.eiu.edu/herbarium_specimens_byname/21408/thumbnail.jp

Magneto-gyrotropic photogalvanic effect and spin dephasing in (110)-grown GaAs/AlGaAs quantum well structures

We report the magnetogyrotropic photogalvanic effect(MPGE)in n-doped (110)-grown GaAs/AlGaAs quantum-well (QW) structures caused by free-carrier absorption of terahertz radiation in the presence of a magnetic field. The photocurrent behavior upon variation in the radiation-polarization state, magnetic field orientation, and temperature is studied. The developed theory of MPGE describes well all experimental results. It is demonstrated that the structure inversion asymmetry can be controllably tuned to zero by variation in the delta-doping layer positions. For the in-plane magnetic ield the photocurrent is only observed in asymmetric structures but vanishes in symmetrically doped QWs. Applying time-resolved Kerr rotation and polarized luminescence we investigate the spin relaxation in QWs for various excitation levels. Our data confirm that in symmetrically doped QWs the spin-relaxation time is maximal; therefore, these structures set the upper limit of spin dephasing in GaAs/AlGaAs QWs