Phonons in Quantum Dots and Their Role in Exciton Dephasing

Abstract

The acoustic phonon spectrum is significantly modified for embedded quantum dots by inhomogeneous change of material propertiesand intrinsic strain. The change of the local elastic properties due to strain is calculated employing density functionaltheory and used as input for phonon calculations within continuum elasticity model. It is demonstrated that overall the exciton--phononcoupling strength is reduced, characteristic oscillations appear in the excitonic polarization, and the spectral broadbandis modified compared to a bulk phonon assumption. The zero phonon line broadening is discussed in terms of real and virtualphonon-assisted transitions between different exciton levels in a quantum dot. A microscopic theory of the excitonic multilevelsystem coupled to acoustic phonons is developed, and the full time-dependent polarization and absorption are calculated usingthe cumulant expansion. Examples are given for dephasing of optical excitations in single and vertically coupled quantum dots.