Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 85: Poster Session II

HL 85.32: Poster

Thursday, March 17, 2011, 18:00–21:00, P4

Generation of coherent and incoherent LO phonons by optical excitation of electrically biased quantum wells — •Thomas Papenkort¹, Tilmann Kuhn¹, and Vollrath Martin Axt² — ¹Institut für Festkörpertheorie, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany — ²Institut für Theoretische Physik III, Universität Bayreuth, 95440 Bayreuth, Germany

Coherent phonons in solids can be generated by optical excitation in a number of different ways, which depend on the material, its structure and the excitation conditions. Although it is the electronic subsystem which the light field predominantly couples to, its detailed characteristics and dynamics can often be left out when explaining the mechanism of phonon generation. In this contribution we will focus on the opposite case where the dynamics of the electronic subsystem plays a vital role to the generation of coherent phonons. An example is the resonant generation of coherent phonons in quantum wells as observed in recent experiments by Mizoguchi et al. [Appl. Phys. Lett. 94, 171105 (2009)], in which a strong coherent phonon amplitude has been achieved by tuning an electronic quantum beat to the LO phonon frequency. We show quantum kinetic calculations of the electronic and phononic dynamics in an optically driven quantum well. We find that the resonant mechanism is very efficient in generating coherent phonons when compared to other mechanisms, but still most of the energy goes into incoherent phonons. Our model also reproduces the limiting cases of phonon generation in which an effective direct coupling of phonons and light field can be assumed.