Coherent dynamics in InGaAs quantum dots and quantum dot molecules

• Published in: Physica. E, Low-dimensional systems & nanostructures Low-dimensional systems & nanostructures, 2005-02, Vol.26 (1), p.400-407
• Main Authors: Langbein, W., Borri, P., Woggon, U., Schwab, M., Bayer, M., Fafard, S., Wasilewski, Z., Hawrylak, P., Stavarache, V., Reuter, D., Wieck, A.D.
• Format: Article
• Language: English
• Subjects: Biexcitons; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Coupled quantum dots; Dephasing; Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Exciton fine-structure; Four-wave mixing; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Physics; Quantum dots
• ISSN: 1386-9477; 1873-1759
• DOI: 10.1016/j.physe.2004.08.004

We measure the dephasing time of the exciton ground state transition in InGaAs quantum dots (QD) and quantum dot molecules (QDM) using a sensitive four-wave mixing technique. In the QDs we find experimental evidence that the dephasing time is given only by the radiative lifetime at low temperatures. We demonstrate the tunability of the radiatively limited dephasing time from 400 ps up to 2 ns in a series of annealed QDs with increasing energy separation of 69–330 meV from the wetting layer continuum. Furthermore, the distribution of the fine-structure splitting ℏ δ 1 and of the biexciton binding energy ℏ δ B is measured. ℏ δ 1 decreases from 96 to 6 μ eV with increasing annealing temperature, indicating an improving circular symmetry of the in-plane confinement potential. The biexciton binding energy shows only a weak dependence on the confinement energy, which we attribute to a compensation between decreasing confinement and decreasing separation of electron and hole. In the QDM we measured the exciton dephasing as function of interdot barrier thickness in the temperature range from 5 to 60 K. At 5 K dephasing times of several hundred picoseconds are found. Moreover, a systematic dependence of the dephasing dynamics on the barrier thickness is observed, showing how the quantum mechanical coupling in the molecules affects the exciton lifetime and acoustic-phonon interaction.