Lateral electronic coupling among self-assembled semiconductor quantum dots promoted by adjoining tunnel-coupled quantum-well potentials

We study lateral electronic coupling among self-assembled In
_0.5
Ga
_0.5
As quantum dots (QDs), which is promoted by adjoining tunnel-coupled In
_0.1
Ga
_0.9
As quantum-well (QW) potentials. The resultant collective electron and its spin dynamics at the coupled excited states in the QDs, virtually via the QW potential, are revealed by means of spin-resolved transient photoluminescence (TRPL). These QD excited states spread over those hybrid nano-systems composed of the coupled QDs and QW, which are elucidated by wavefunction calculations and then comparted to the TRPL results. The existence of the adjoining QW can induce stronger coupling among QDs in the lateral direction, where thicker QWs make stronger inter-dot coupling. We observe that circularly polarized TRPL, reflecting the spin dynamics, is dynamical functions of spin-polarized electron transfer among the coupled QDs and discrete-state filling in the QDs as well as spin relaxation in individual QDs. As a result, temporally stable high spin polarizations higher than 60 % are achieved in the QDs, sustained by selective transfer of minority spins into lower-energy spin states.