Size-dependent activation energy and carrier dynamics in Cd_xZn_1-xTe/ZnTe quantum dots on Si substrates

We investigate the size-dependent activation energy and carrier dynamics in Cd_xZn_1-xTe /ZnTe quantum dots (QDs) grown on Si substrates. The excitonic peak corresponding to transitions from the ground electronic subband to the ground heavy-hole band in Cd_0.6Zn_0.4Te/ZnTe QDs shifts to a lower energy with increasing Cd_0.6Zn_0.4Te thickness owing to an increase in the size of the QDs. The activation energy of the electrons confined in the Cd_0.6Zn_0.4Te /ZnTe QDs, as obtained from the temperature-dependent photoluminescence (PL) spectra, increases with increasing Cd_0.6Zn_0.4Te thickness owing to an enhancement of the quantum confinement effect resulting from an increase in the energy difference between the electronic state and the conduction band edge. The carrier dynamics of Cd_0.6Zn_0.4Te /ZnTe QDs is studied using time-resolved PL measurements, which shows a longer exciton lifetime for Cd_0.6Zn_0.4Te /ZnTe QDs with increasing Cd_0.6Zn_0.4Te thickness. This behavior is attributed to the reduction of the exciton oscillator strength resulting from a strong built-in electric field in the larger QDs.