Exciton coherence in semiconductor quantum dots

Abstract

The coherent dynamics of excitons in InAs quantum dots (QDs) was investigated in the tekcoromunication wave-length range using a transient four-wave mixing technique. The sample was fabricated on an lnP(311)B substrate using strain compensation to control the emission wavelength, This technique also enabled us to fabricate a 150-layer stacked QD structure for obtaining a high S/N in the four-wave mixing measurements, although no high-sensitive heterodyne detection was carried out. The dephasing time and transition dipole moment were precisely estimated from the polarization dependence of signals, taking into account their anisotropic properties. The population lifetimes of the excitons were also measured by using a polarization-dependent pumpprobe technique. A quantitative comparison of these anisotropics demonstrates that in our QDs, non-radiative population relaxation, polarization relaxation and pure dephasing are considerably smaller than the radiative relaxation. A comparison of the results of the four-wave mixing and pump-probe measurements revealed that the pure dephasing could be directly estimated with an accuracy of greater than 0.1 μeV by comparing the results of four-wave mixing and pump-probe measurements. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.