Revealing exciton dephasing and transport dynamics in semiconductor quantum well - quantum dot systems using optical 2D Fourier transform spectroscopy

Abstract

Exciton dephasing and relaxation dynamics are studied in a GaAs quantum dot ensemble using optical twodimensional Fourier transform spectroscopy. We measure the temperature and excitation-density dependence of the exciton ground-state homogeneous lineshape of quantum dots within the ensemble and show that acoustic phonon sidebands are absent. The linewidth increases nonlinearly with temperature from 6 to 50 K and the behavior is well-described by an Arrhenius equation with an offset. The absence of a phonon-activation peak in the spectra reveals that elastic exciton-phonon scattering is the primary dephasing mechanism and the results can be explained qualitatively using an extension of the independent Boson model that includes quadratic coupling in the phonon displacement coordinates. At temperatures ≥ 35 K, spectral features associated with phonon-assisted population transfer of excitons out of the quantum dots and into quantum wells states begin to appear.