Ultrafast dynamics in ZnO/ZnMgO multiple quantum wells

We have investigated carrier relaxation and exciton recombination dynamics in ZnO/ZnMgO multiple quantum wells using femtosecond pump–probe techniques at room temperature. For a probe energy above the band gap, the hot carriers exhibit an effective relaxation by longitudinal optical phonon scattering with a cooling time of 700–850 fs. By detecting the emission near the band-gap, a longer decay time of a few picoseconds was observed which is attributed to acoustic phonon scattering. As the probe energy is decreased further, the decay time continues to increase due to the transitions of exciton recombination or localized carrier recombination. (Some figures in this article are in colour only in the electronic version)