Chemical equilibrium between excitons, electrons, and negatively charged excitons in semiconductor quantum wells

The principle of chemical equilibrium is found to govern formation of negatively charged excitons (X-) by excitons (X) and free electrons (e(-)). An optical spectroscopy study of undoped CdTe/Cdo(0.88)Mn(0.12)Te double quantum wells (QW's) revealed formation of a negatively charged exciton state in the thicker QW due to the interwell tunneling of photoexcited electrons. A peculiar, nonmonotonic behavior of the ratio of X to X- densities as a function of the excitation density evidenced that the chemical law of action of masses corresponding to the reaction X+e(-)double left right arrow X- is fulfilled. [S0163-1829(98)06547-3].