Optical Orientation of Excitons in a Longitudinal Magnetic Field in Indirect-Band-Gap (In,Al)As/AlAs Quantum Dots with Type-I Band Alignment

Exciton recombination and spin dynamics in (In,Al)As/AlAs quantum dots (QDs) with indirect band gap and type-I band alignment were studied. The negligible (less than 0.2 mu eV) value of the anisotropic exchange interaction in these QDs prevents the mixing of the excitonic basis states and makes the formation of spin-polarized bright excitons possible under quasi-resonant, circularly polarized excitation. The recombination and spin dynamics of excitons are controlled by the hyperfine interaction between the electron and nuclear spins. A QD blockade by dark excitons was observed in the magnetic field, that eliminates the impact of nuclear spin fluctuations. A kinetic model which accounts for the population dynamics of the bright and dark exciton states as well as for the spin dynamics was developed to quantitatively describe the experimental data.

Automated summary

This study investigated exciton recombination and spin dynamics in (In,Al)As/AlAs quantum dots with indirect band gap and type-I band alignment. The anisotropic exchange interaction in these quantum dots was found to be negligible, enabling the formation of spin-polarized bright excitons under quasi-resonant, circularly polarized excitation. The recombination and spin dynamics of excitons were controlled by the hyperfine interaction between the electron and nuclear spins. A kinetic model was developed to quantitatively describe the experimental data, taking into account the population dynamics of the bright and dark exciton states as well as the spin dynamics.