Berlin 2012 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 6: Ge/Si I
HL 6.2: Talk
Monday, March 26, 2012, 09:45–10:00, EW 203
Picosecond hole scattering and cooling dynamics in Ge/SiGe quantum wells. — •Kolja Kolata1, Sebastian Imhof2, Niko Köster1, Giovanni Isella3, Daniel Chrastina3, John E. Sipe4, Angela Thränhardt2, and Sangam Chatterjee1 — 1Fachbereich Physik, Philipps Universität Marburg, Germany — 2Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Germany — 3Dip. di Fisica del Politecnico di Milano, L-NESS, Polo di Como, Italy — 4Department of Physics, University of Toronto, Canada
We investigated the hole scattering and cooling dynamics in Ge/SiGe quantum wells on a picosecond time scale. Time-resolved pump-probe experiments show an efficient scattering process between the electron and hole systems in the L- and Γ-valley, respectively. The Ge quantum wells are excited 10 meV above the band edge and probed with a white-light supercontinuum. After optical excitation, the electrons scatter from the Γ-valley into the lower lying L-valleys within a few hundreds of fs. At later times, only the hole system is investigated as photons can only access vanishing momenta. We observe a hot hole system with a temperature far beyond what is expected from the excess energy of the excitation. The additional heating is due to efficient energy transfer from the electron system in the L-valley which heats the hole-system in the Γ-valley mediated by Coulomb-interaction. The dependence on excitation energy as well as carrier density support this explanation. Our findings are corroborated by semiconductor Bloch equations calculations of the absorption spectra for various hole-system carrier-densities and temperatures.