Optical Spectroscopy on Single Quantum Dots: Charged Excitons

Abstract

Single self-assembled quantum dots are among the most widely studied systems in the field of modern solid state spectroscopy. Neutral multi-exciton complexes have been investigated in quantum dots by power dependent photoluminescence spectroscopy. The experimental preparation of specific charged exciton states in a single quantum dot can be realized by bias controlled single electron charging and can be probed by optical spectroscopy. With respect to neutral single exciton configurations, the optical response of charged exciton complexes is modified due to few particle interaction of the carriers confined in the quantum dot. As a consequence of these renormalization effects we observe different emission energies for the neutral, single, and double charged excitons in single quantum dot spectroscopy. A quantitative comparison of the experimentally determined binding energies for single and double charged excitons with theoretical model calculations demonstrates a substantially stronger confinement of the hole wave function with respect to the electron wave function. The observation of spin dependent tunneling from singlet and triplet states at high magnetic fields nicely demonstrates that spin related phenomena can be considerably enhanced in quantum dots. The influence of the sample structure can be seen by the appearance of charge equilibrium and non-equilibrium states in bias dependent photoluminescence spectra of different single quantum dot photodiodes.