Exciton g-Factors, Diamagnetic Shifts, and Exchange Splittings in Quantum Dots in GaAs Quantum Wells

Abstract

Excitons localised in the random interfacial potential that occurs naturally in GaAs quantum wells (QWs) have been studied. The states are those of random quantum dots (QDs), and give narrow, homogeneously broadened photoluminescence emission lines; this makes them ideal for the study of small effects such as splittings and shifts induced by a magnetic field and exchange interaction. We show that the random nature of the interfacial potential leads to a distribution of both g-factor and diamagnetic shift, which we determine for individual QD excitons. Although there is little systematic correlation of g-factor with position in the inhomogeneous distribution, there are systematic correlations between the diamagnetic shift and the exchange splitting. These results are consistent with highly localised states showing symmetry lower than that of the QW, and an enhanced exchange interaction. We analyse the results in terms of a spin Hamiltonian which treats the heavy-hole excitons as an effective spin-1/2 system.