Field dependence of carrier capture in GaAs/AlAs/AlGaAs double-barrier quantum well structures.

We report on electron and hole capture times in n-type GaAs/AlAs/Al0.3Ga0.7As double-barrier quantum well (DBQW) structures in an electric field applied perpendicular to the layers. We have measured the time-dependent photoluminescence (PL) originating from the GaAs wells and the Al0.3Ga0.7As barrier layers. The experimental capture times are obtained from least-squares fits of appropriate model functions to the observed PL transients. We have theoretically determined electron capture times for the investigated DBQWs, by calculating the electron wavefunctions and taking into account various scattering processes, including impurity scattering, optical phonon-assisted tunnelling and intervalley scattering. We find evidence that electron capture occurs by Gamma -X intervalley transfer via X-point subbands localized in the AlAs layers.