Münster 1999 – scientific programme

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HL: Halbleiterphysik

HL 17: Quantenpunkte und Quantendr
ähte II

HL 17.9: Talk

Tuesday, March 23, 1999, 12:30–12:45, H4

Ultrafast dynamics of InGaAs/GaAs quantum dot amplifiers under femtosecond optical excitation — •P. Borri¹, W. Langbein¹, J.M. Hvam¹, F. Heinrichsdorff², M.-H. Mao², and D. Bimberg² — ¹Mikroelektronik Centret, Technical University of Denmark, DK-2800 Lyngby, Denmark — ²Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin

Semiconductor lasers with an active medium containing zero-dimensional structures are expected to show superior performances, like ultrahigh gain, low and temperature-independent threshold current and chirp-free operation. Semiconductor quantum dot lasers have been recently fabricated, allowing for an experimental test of their performance.
We have measured the optical properties of triple stacked MOCVD grown InGaAs/GaAs quantum dot amplifiers at room temperature (RT) using femtosecond pulses. Single pulse propagation, heterodyne pump-probe and four-wave mixing techniques have been used. These techniques allow us to measure stationary properties, like modal gain and transparency current, and , for the first time in quantum dot devices, dynamical properties like dephasing time and carrier escape/capture times from/into the dots. We find that gain and absorption factor are comparable as expected in a two level system. We measure dephasing times ∼ 200 fs at RT for non-inverted systems, and faster than 70 fs for the inverted case. Escape times of ∼ 4 ps and capture times less than 0.3 ps are deduced from pump-probe experiments.