Short-period transient grating measurements of perpendicular over-barrier diffusion in GaAs/AlGaAs multiple quantum wells

A short-period transient grating technique is used to study perpendicular (or cross-well) transport as a function of lattice temperature in a GaAs/Al0.3Ga0.7As multiple quantum well with barriers that are sufficiently thick (10 nm) to ensure that tunneling is negligible. The grating decay time is observed to increase dramatically as the temperature is decreased, consistent with the need to thermally activate carriers from the wells; however, thermal activation alone will not account for the observed temperature dependence. The measured temperature dependence of the perpendicular transport, however, can be fit by including the temperature dependence of the above-barrier diffusion coefficients as well as the temperature dependence of the thermal activation. These fits to the data, which assume diffusion limited by polar-optical-phonon scattering, yield diffusion coefficients typical of those measured in AlGaAs alloys.