Exciton-LO phonon dynamics in $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots: Effects of zone-edge phonon damping

The dynamics of an exciton-LO phonon system after an ultrafast optical excitation in an $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dot is studied theoretically. Influence of anharmonic phonon damping and its interplay with the phonon dispersion is analyzed. The signatures of the zone-edge decay process in the absorption spectrum and time evolution are highlighted, providing a possible way of experimental investigation on phonon anharmonicity effects.

Figure 1

Single-mode line shape (left) and temporal evolution (envelope of LO oscillations, right) for three modes with wave vectors as shown, for ${\Omega }_0-{\Omega }_{{\mathit{k}}_{\mathrm{L}}}-{\omega }_{{\mathit{k}}_{\mathrm{L}}}=-0.5\mathrm{meV}$.

Figure 2

(a) The hypothetical line shape of the LO phonon replica of the ground exciton state without anharmonic damping (broadened only due to dispersion) and the corresponding envelope of LO phonon beats (line) compared to the exact result (squares). (b)–(d) The line shapes of the phonon replicas corresponding to the ground state (dashed lines) and to the first excited, optically inactive state (solid lines) and the corresponding envelope of the phonon beats for three values of the band overlap as shown. The central frequency ${\omega }_0$ corresponds to $E_n+{\Omega }_0$ for each line. In plots (b) and (c) it is assumed that the zone-edge process contributes 90% of the decay probability. In (d), where the zone-edge process is forbidden, the anharmonic LO-TA coupling is the same as in (c).