Effect of Phonon Confinement on Optical Phonon-Mediated Carrier Capture into CdSe/ZnS Quantum Dots

Abstract

Electron capture induced by carrier heating in the CdSe/ZnS spherical quantum dot–quantum well structure is studied theoretically. The capture rate has been calculated by taking into account the phonon confinement effect. Numerical results for the capture rate as a function of dot radius, lattice temperature, and electron density in the CdSe/ZnS/H2O quantum dot (QD) system are obtained and discussed. It has been shown that the capture rate of an electron from the barrier region to the quantum dot ground state due to the emission of confined or interface optical phonons exhibits strong resonances versus dot radius. Our results reveal that the capture time is larger than 1 ns across broad ranges of quantum dot radius. We have found the increase of the capture rate due to emission of LO1 as well as IO/SO phonons with increasing temperature. However, for structures with lower electron densities (n ≤ 1016 cm−3), the monotonic behavior of the capture rate in case of IO/SO phonon interactions is broken and a local maximum in the temperature dependence appears. In contrast to the GaAs/AlAs spherical quantum dot–quantum well structure, the capture rate in CdSe/ZnS/H2O QDs is very strongly dependent on the electron density.