Regensburg 2004 – scientific programme

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HL: Halbleiterphysik

HL 42: Quantenpunkte und -dr
ähte: Optische Eigenschaften II

HL 42.5: Talk

Thursday, March 11, 2004, 16:15–16:30, H13

The Nature of the Excitonic Ground State in coupled QD Molecules — •H. J. Krenner, M. Sabathil, W. Prestel, D. Schuh, M. Bichler, J. J. Finley, and G. Abstreiter — Walter Schottky Institut, TUM, Am Coulombwall 3, 85748 Garching

We present a combined theoretical and experimental investigation of excitonic states in individual QDMs subject to axial electric fields (F). Theoretical calculations of the interband spectra including a full treatment of strain and Coulomb interactions, demonstrate that the electron dot-dot coupling is significantly stronger than for holes. This gives rise to a field driven transition of the nature of the excitonic ground state between optically active (direct) and optically inactive (indirect) states.

We have experimentally tested this prediction of a field driven anticrossing by performing photoluminescence on single QDMs. Over the field range for which the ground state is predicted to be dark, a characteristic emission multiplet is observed from each QDM following quasi resonant excitation into the wetting layer. This structure is attributed to optically active few particle states in the nominally dark QD, a conclusion supported by experiments using non-resonant excitation above the barrier band gap where only one emission line is observed. Furthermore, indirect excitons are shown to exhibit a strongly anomolous linear Stark shift consistent with a large intrinsic e-h separation (∼2-3 nm).