Electron-hole relaxation through optical-phonon emission in CdTe/ZnTe quantum dots

We present a study of ZnCdTe quantum dots (QDs) embedded in Zn-rich ZnCdTe quantum wells (QWs). The Cd-rich ZnCdTe islands are confined along the growth direction by pure ZnTe barriers and laterally by Zn-rich ZnCdTe QWs. Using a time-resolved pump and probe technique, we analyse the phonon emission-cascade in QWs governing, after non-resonant optical excitation in the QWs, the energy relaxation of electron-hole pairs towards self-organized QDs. Since electron-hole pairs thermalize only by emission of an integer number of longitudinal-optical phonons, at the end of the cascade, the QDs become selectively populated. We thus determine the mean value of the optical-phonon emission time. Then, for longer time delays, we observe the population relaxation dynamics of the selected quantum dots.