only formed by photoexcited carriers.

The Rayleigh SAWs (with wavelength ${\lambda_\mathrm{SAW}}$=2.8 $\mu$m corresponding to a SAW frequency ${f_\mathrm{SAW}}=1$ GHz at helium temperatures) were electrically excited along a $<$100$>$ surface direction by applying a radio-frequency (RF) signal to interdigital transducers (IDTs) deposited on piezoelectric ZnO islands. These SAWs do not carry a piezoelectric field outside the IDT region, thus preventing field-induced exciton dissociation [@Ref21]. Their strain field creates, via the deformation potential interaction, the moving type-I modulation of the CB and VB band edges of the DQW [@Ref22] displayed in Fig. \[Fig1\](b). Here, E$_{g,min}$ (E$_{g,max}$) denotes the minimum (maximum) bandgap at the SAW phases of largest tensile (compressive) strain. Photoexcited IXs are captured close to the regions of E$_{g,min}$, which move with the acoustic velocity ${v_\mathrm{SAW}}$ [@Ref21]. The confinement of the electron and the hole at the same lateral (i.e., along the surface) coordinate prevents exciton dissociation, thus making this approach qualitatively different from charge transport by the type-II bandgap modulation induced by the piezoelectric SAWs. The depth of the DQW structures was selected in order to obtain a type-I potential with approximately equal modulation amplitudes for the conduction and valence bands.[@Ref23]

The transport of IXs by the SAW strain field 