Effect of phonon confinement on one- and two-polar optical phonon capture processes in quantum dots

Abstract

The electron capture in spherical quantum dot–quantum well structure is studied theoretically. The capture rate in one- and two-polar-optical-phonon-mediated capture processes has been studied by taking into account the phonon confinement. We have derived the explicit analytic expressions for carrier capture rates which can be conveniently applied to practical calculations for the spherical quantum dot systems. The numerical results of the capture rate as function of dot radius, lattice temperature and electron density in GaAs/AlAs QD systems are obtained and discussed. The dependence of the carrier capture rate for a fixed dot radius shows a maximum as a function of carrier density. It is shown that the capture rate of an electron from the barrier region to the quantum dot ground-state, via emission of one and two phonons, exhibits the existence of the bands of dot radii where capture is energetically allowed. We found that the height of the capture rate peaks obtained for one-phonon assisted processes is lowered as QD radius decreases when the phonon confinement is taken into account. The capture rates due to emission single and two optical phonon modes are compared. Carrier capture is shown to proceed with rates as high as 1010s−1 at temperatureT>100K. A short capture time is also achieved for a low carrier density.