Charged Exciton Emission Research Articles

Charged excitons in single CdTe quantum dots

Optical emission from individual n-type modulation-doped CdTe quantum dots (QDs) is presented. Exciton, biexciton and negatively charged exciton emission lines are identified in the micro-photoluminescence spectra. All these few-particle species are exposed to randomly fluctuating electric fields attributed to charges trapped in the vicinity of the QD. The resulting quantum-confined Stark effect, characteristic for each QD, is analyzed in detail. The correlation between the emission energies and the integrated intensities of the neutral and charged exciton permit one to confirm the identification of the charged species. The binding energies of the biexciton and charged exciton are found to sharply decrease with the magnitude of the local electric field.

Experimental measurement of microwave-induced electron spin-flip time

The electron spin resonance (ESR) is optically detected by monitoring the microwave-induced changes in the circular polarization of the neutral exciton (X) and the negatively charged exciton (X−) emission in CdTe quantum wells with low density of excess electrons. We find that the circular polarization of the X and X− emission is a mapping of the spin polarization of excess electrons. By analyzing the ESR-induced decrease in the circular polarization degree of the X emission, we deduce the microwave-induced electron spin-flip time >0.1 μs, which is much longer than the recombination time of X and X−. This demonstrates that the optically detected ESR in type I quantum wells with low density of excess electrons does not obey the prerequisite for the conventional optically detected magnetic resonance.