All-optical generation and coherent control of ultrafast shift and injection currents in GaAs quantum well structures

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Generating electrical currents in semiconductors by purely optical means, i.e., without electrical bias fields, using femtosecond laser excitation has not only become a powerful means for studying nonlinear coherent light-matter interaction but also opens promising options for THz electromagnetic wave generation. Different physical processes, like optical rectification, shift current generation, and injection current generation, have been identified as the sources for optically-induced currents. All these effects represent coherent second-order nonlinear optical interactions. While the generation of injection currents is symmetry forbidden in bulk GaAs, we have recently demonstrated that in especially designed, i.e., (110)-oriented, GaAs/AlGaAs quantum well structures injection currents can be generated. Even more surprising and unexpected was our finding that injection currents could be measured for resonant excitation of the lowest exciton resonances. The overall goal of this proposal is to analyze experimentally and theoretically the conditions under which the generation of different types of injection currents by resonant exciton excitation is possible. A sound microscopic theoretical description of the so far not identified underlying physical processes, that is based on extended semiconductor Bloch equations, will be developed and analyzed. Our joint investigations will provide new insight in the fundamental mechanisms governing nonlinear light-matter interactions and all-optical current generation in semiconductor nanostructures.