Dynamic control of photoluminescence polarization properties in GaAs/AlAs quantum wells by surface acoustic waves

We have investigated the dynamic polarization properties of photoluminescence (PL) spectra in GaAs/AlAs quantum wells (QWs) modulated by surface acoustic waves (SAWs) in various configurations. One-dimensional standing SAWs, which are formed by the interference of two counterpropagating SAW beams, exhibit emission energy oscillations due to strain-induced band gap modulation. When the band gap energy reaches its minimum value, the PL spectra exhibit the strongest polarization anisotropy, with preferential emission along the direction perpendicular to SAW propagation. Two-dimensional SAWs formed by the interference between two orthogonally propagating SAW beams also cause the emission energy to oscillate, while no polarization anisotropy appears. In contrast, a pi/2 relative phase difference, which is electrically introduced between the two SAWs, significantly alters both the PL spectra and the polarization anisotropy. The oscillation of the emission energies disappears and the polarized direction changes every quarter SAW period. These SAW phase-dependent changes in the polarization properties are explained by considering the exciton motion under the quadrupolelike SAW modulation, which is formed by the two orthogonal unbalanced standing SAWs with a phase difference of pi/2.