Carrier Relaxation of ZnCdSe/ZnSe Quantum Wells

The energy relaxations of Zn0.91Cd0.09Se multiquantum wells and epilayer structures were studied with an ultrafast time-resolved photoluminescence apparatus. The increase in the rise time of photoluminescence with decreasing photon energy and the redshift of the peak energy of time-resolved photoluminescence spectra with the delay time are attributed to the band-filling effect and energy relaxation of hot carriers. The derived carrier temperature decreases rapidly within the first 10 ps after photoexcitation and at a much slower rate thereafter. The fast carrier cooling can be explained by the longitudinal optical (LO) phonon emissions by carriers through the Fr?hlich interaction. The obtained effective scattering times of carrier and LO phonons are comparable to the theoretical prediction of 20 fs for multi-quantum well (MQW) of 20 nm well thickness and the epilayer. The slow carrier capture process may account for the long effective scattering time of 35 fs for the MQWs of 5 nm well thickness.