Single photon sources from InP based colloidal quantum dots

Abstract

CdSe based colloidal quantum dots are extensively studied for a variety of applications including the single photon emission at room temperature [1, 2]. While the blinking has been considerably reduced in CdSe quantum dots, the purity of single photon emission has been elusive at higher intensities due to the contribution of multiple excitons. We observe that the newly synthesized Cd-free InP based quantum dots have similar optical properties to CdSe. The broader ensemble spectra of InP was earlier believed due to the broader single dots but our characterization on the InP/ZnSe prove the inhomogeneity by the presence of narrow single dot spectra. The single quantum dots also exhibit strong antibunching (g2(0)<0.02) at intensities below and above the saturation level proving the nature of single quantum emitter and a two-level system. InP/ZnSe core/shell quantum dot has a type I energy level structure where both the charge carriers are confined in the core itself. The strong antibunching reveals that the probability of radiative recombination with more than one exciton is very low. We believe the stronger Auger rate of 70 ps is the preferred route for the multiple excitons, ultimately emission coming only from the single exciton. The presence of faster Auger process was earlier thought to be responsible for the presence of dark states leading to more blinking in the emission of the quantum dots [2]. But our characterization results on this quantum dot are novel which show suppressed blinking and also strong antibunching due to the efficient Auger process at the same time.