Regensburg 2013 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 87: Goup IV elements and their compounds II
HL 87.5: Vortrag
Donnerstag, 14. März 2013, 16:45–17:00, H15
Dephasing in Ge/SiGe quantum wells measured by means of coherent oscillations — •Kolja Kolata1, Niko S. Köster1, Alexey Chernikov1, Michael J. Drexler1, Eleonora Gatti2, Stefano Cecchi3, Daniel Chrastina3, Giovanni Isella3, Mario Guzzi2, and Sangam Chatterjee1 — 1Philipps-Universität Marburg — 2L-NESS, Università di Milano Bicocca — 3L-NESS, Polo di Como
In general, all coherent effects in optically excited materials depend crucially on the dephasing of the addressed states. Therefore, knowing the duration of the coherence and understanding the dephasing mechanisms is mandatory in order to interpret coherent effects correctly. Dephasing mechanisms are often summarized in the dephasing time which is also used as a phenomenological damping parameter in theoretical descriptions. Ge/SiGe heterostructures as a material system are especially interesting for dephasing studies since they exhibit strong nonlinear coherent responses such as the giant dynamical Stark effect. We present a dephasing time analysis of the three lowest excitonic resonances in Ge/SiGe quantum well samples for the temperatures down to 7K by coherent oscillations spectroscopy (COS). The results are compared to the line widths of the excitonic resonances determined by linear absorption measurements. Strikingly, the lowest direct-gap transition in the best quality sample is dominated by homogeneous broadening over the entire investigated temperature range. This is explained by the fast inter-valley scattering of the electrons which leads to intrinsically short dephasing times of merely 300 fs as an upper limit.