Rapid carrier relaxation in ${\mathrm{In}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dots characterized by differential transmission spectroscopy

Carrier relaxation in self-organized ${\mathrm{In}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dots is investigated by time-resolved differential transmission measurements. The dots have a base dimension of around 14 nm and a height of 7 nm, leading to an average energy separation of the ground and first excited electronic states much greater than the LO-phonon energy, so the phonon-mediated electron relaxation is expected to be slow. Our measurements indicate that, even at low carrier densities (less than one electron-hole pair per dot), the electron and hole relaxation time constants are 5.2 and 0.6 ps, respectively; this indicates a lack of any “phonon bottleneck” and is consistent with a model of electrons scattering from holes which can relax rapidly via phonon emission.