Dynamics of resonant and nonresonant electron tunneling in double-quantum-well structures under electric fields

Tunneling processes of two-dimensional electrons between two quantum wells (QW’s) and those from one QW to unconfined three-dimensional states outside through another QW are investigated in various double-QW structures by time-resolved photoluminescence (PL) measurements. Electric fields ${\mathit{F}}_{\mathit{z}}$ across the double-QW structures are applied to realize on- and off-resonance conditions, and the electron lifetime and time-integrated PL intensity are measured as functions of the field ${\mathit{F}}_{\mathit{z}}$. The experiment has demonstrated the enhancement of the tunneling rate near the resonance and its reduction under the off-resonance condition. The measured tunneling rates are compared with various theoretical models to show that a scattering-assisted process plays a dominant role in interwell tunneling when the ground levels of the two QW’s are nearly resonant. At a certain bias voltage above resonance, a distinct reduction of the electron lifetime is observed and is attributed to LO-phonon-assisted tunneling into the other QW.