Regensburg 2010 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 55: Quantum Dots and Wires, Optical Properties IV: Spin

HL 55.6: Vortrag

Donnerstag, 25. März 2010, 15:15–15:30, H14

Long excitonic spin relaxation in InAs/AlAs quantum dots — •Birgit Brinkmann¹, T. S. Shamirzaev², J. Debus¹, D. Dunker¹, D. R. Yakovlev¹, and M. Bayer¹ — ¹Experimentelle Physik II, TU Dortmund, 44227 Dortmund, Germany — ²Institute of Semiconductor Physics, pr. Lavrentieva, 13, Novosibirsk 630090, Russia

We investigated the excitonic spin relaxation in self-assembled InAs quantum dots, embedded in an AlAs matrix, by means of time-resolved, circularly polarized photoluminescence.

The atomic-like electronic structure of self-assembled quantum dots suppresses not only elastic but also inelastic processes of spin relaxation mechanisms, thus increasing the exciton spin relaxation time τ_s. The experimental determination of τ_s is typically inhibited by the short exciton lifetime of a few nanoseconds. However, the novel InAs/AlAs quantum dot system, characterized by the lowest electron state at the direct Γ or indirect X conduction band minima, exhibits exciton lifetimes of several milliseconds. At a temperature of 1.8 K the exciton spin relaxation time τ_s is in the range of 100 µs. It strongly depends on the optical excitation density, temperature and quantum dot size.

Differences between the direct and indirect bandgap transitions have been observed in the temporal evolution of the non-equilibrium exciton spin-orientation induced by an external magnetic field or excitation with circularly polarized light. Spectral and temperature dependencies of photoluminescence kinetics are explained in terms of an electron redistribution between long-lived indirect and short-lived direct states of the quantum dot conduction band.