Tunneling Dynamics and Resonant Coupling of Electrons in GaAs/AlAs Coupled Double Quantum Well Structures under Electric Fields

Abstract

Resonant tunneling(RT) phenomenon in double-barrier(DB) heterostructure[1,2] has a conceptual similarity to a transmission of optical waves in Fabry-Perot (FP) resonator and involves time delay. Its dynamics should be investigated since they limit the ultimate speed of RT devices. Such a study will also clarify similarities and differences between electronic and optical waves. In our previous work[3], we investigated the tunneling escape process of electrons from AlAs/GaAs/AlAs DBRT structures. The measured escape rate was well explained by the idealized theory of FP-like model, which predicts the tunneling escape time τ in DBRT structures is given by |t| 2vk/Lw, when |t|2 ≪1, where t is the transmission coefficient through the barrier, vk is the group velocity of electrons and Lw is the well width. This predicted escape time is equal to the one calculated by the sequential tunneling model, suggesting that the tunneling escape time is not strongly dependent on the coherency of electron waves. This simple relation may not hold for the tunneling process between quantum wells(QW), where resonant coupling effect plays a more sophisticated role. To clarify the resonant tunneling phenomena between QWs, we report, in this paper, our study on electron dynamics in several different double GaAs QW structures separated by thin AlAs barrier, where the coupling condition between QWs was varied by electric fields. Tunneling process was studied at ~20K by measuring time resolved photoluminescence(PL). Picosecond pulses of a mode-locked dye laser were used to generate electron hole pairs in QWs, and the subsequent PL from particular QWs was monitored by a streak camera to determine the time variation of electron density in the QWs. Note that the electrons are lost either by recombination (radiative[4] and nonradiative) and/or by tunneling process. Since the mass of heavy hole is quite heavy, hole tunneling can be neglected at least in the initial phase of tunneling.