Shift currents from symmetry reduction and Coulomb effects in (110)-orientatedGaAs∕Al0.3Ga0.7Asquantum wells

Abstract

We report on the observation of an additional shift current tensor element by interband excitation of undoped (110)-oriented $\mathrm{GaAs}∕{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ quantum wells with a $150\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ laser pulse. The additional tensor element results from the symmetry reduction of the quantum well structure and shows a strong enhancement and a phase shift at the light-hole exciton transition revealing that shift currents are a sensitive probe of Coulomb effects in semiconductors. Moreover, we show that the overall shift current does not directly follow the envelope of the optical excitation pulse but contains a noninstantaneous contribution.