Heterogeneous confinement in laterally coupled InGaAs/GaAs quantum dot molecules under lateral electric fields

Abstract

We study the electronic and optical properties of laterally coupled InGaAs/GaAs quantum dot molecules under lateral electric fields. We find that the electrons perceive the double-dot structure as a compound single object and tunnel through a basin connecting the dots from underneath. The holes discern two well-separated dots and are unable to tunnel. Through a combination of predictive atomistic modeling, detailed morphology studies, and single-object microphotoluminescence measurements, we show that this peculiar confinement results in an unusual heterogeneous behavior of electrons and holes with profound consequences on optical properties. We find a qualitatively different signal in optical-absorption, emission under resonant, and emission under nonresonant excitations. We explain this behavior by invoking the carriers' dynamics following light absorption.

Coulomb interaction signatures in self-assembled lateral quantum dot molecules

“…The basin structure in between the QD pair could also influence the tunneling strength. 16 The simulations also predict the inverted energy of ( 0 2 0 1 ) and ( 2 0 1 0 ) emissions as a result of the interdot tunneling of the electron in the final state. 19 Our experimental techniques do not allow us to confirm this assignment, but it seems consistent with the fact that the former shows up at smaller bias than the latter in Fig.…”

“…This redshift is one of the distinct PL properties of LQDMs that has been predicted by both pseudopotential 16 and effective mass 17 modeling. In the X + initial state, one electron-hole pair sits in the right QD and the remaining hole in the left QD.…”

“…Consequently, we observe a quasicontinuous Stark shift of the PL line as increasing numbers of electrons occupy the excited states. 16,18 To summarize this section, we have provided a detailed understanding of the charging process of LQDMs with nearly degenerate QDs by comparing experimental PL data with theoretical estimates and logical relaxation dynamics. The observation of energy shifts computationally predicted to arise from electron tunneling provides strong experimental evidence for the existence of tunnel coupling for X + (and possibly X − ) in this system.…”

“…Peng and Bester have used atomistic empirical pseudopotential calculations to calculate the energies of excitons with different charge configurations in InGaAs LQDMs under lateral electric fields. 16 In the recent publication of Royo et al, the optical resonance of neutral and charge excitons in LQDMs was simulated as a function of interdot distance. 17 Both of these papers predicted sensible signatures of tunnel coupling in charged states.…”

Polarization anisotropic luminescence of tunable single lateral quantum dot molecules

“…1(a)) and shows no significant tunnel coupling. 13,27 III. OPTICAL SPECTROSCOPY A. Low-temperature micro-photoluminescence Low-temperature micro-PL measurements were carried out in a helium flow cryostat at 5 K by using an objective lens with NA ¼ 0.45, which results in a focus diameter of about 1.5 lm.…”