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HL: Fachverband Halbleiterphysik
HL 42: Optical Properties of Quantum dots: Theory and Simulation
HL 42.2: Talk
Thursday, February 28, 2008, 09:45–10:00, EW 201
Gain reduction in semiconductor Quantum Dot systems — •Michael Lorke1, Jan Seebeck1, Paul Gartner1, Frank Jahnke1, and Weng Chow2 — 1Institute for Theoretical Physics, University of Bremen — 2Sandia National Laboratories, Albuquerque, New Mexico
For practical application of quantum dots (QDs) in light emitters as well as for fundamental studies of their emission properties, dephasing processes due to carrier-carrier and carrier-phonon interaction play a critical role. They determine the homogeneous linewidth of the QD resonances, limit the coherence properties of QD lasers and their ultrafast emission dynamics, and have a strong influence on coherent optical nonlinearities. A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of a coherent excitation and line-shifts of the interband transitions due to carrier-carrier Coulomb interaction and carrier-phonon interaction are determined from a quantum kinetic treatment of correlation processes which includes non-Markovian effects.
Our quantum kinetic theory predicts a new effect, not found in other gain materials. For large carrier densities, the maximum gain can decrease with increasing carrier density. This behavior arises from a interplay of state filling and dephasing, so that a appropriate treatment of the carrier density dependence of dephasing is necessary. Results for the α-factor for QD systems and a comparison of the peak gain between QDs and quantum wells are will be shown. The presented theory will also be used to determine gain spectra in nitride material systems.