Diamagnetism as a probe of exciton localization in quantum wells.

Abstract

Exciton photoluminescence (PL) is an important technique for the characterization of quantum wells (QW's). We discuss the effect of localization on the diamagnetic energy shift of an exciton in a QW. It is shown how the diamagnetism of an electron in the ground state, with arbitrary geometry, depends on the dimensions of its wave packet. We consider the properties of free excitons in QW's, introducing an effective electron-hole interaction. We use dimensional analysis to relate the finite-barrier problem to the simpler case of perfect confinement. For a bound exciton, localization in the plane of the QW causes the diamagnetism to be smaller than for a free exciton. The effect of localization is not important if the range is much larger than the free-exciton Bohr radius. The exciton diamagnetic shift is reduced by localization in 10 and 20 A\r{} (In,Ga)As/InP QW's grown by solid-source molecular-beam epitaxy. Uncertainty about the value of the free-exciton diamagnetic shift limits the sensitivity of the diamagnetism as a probe of exciton localization. Despite this, the method still provides valuable information on exciton localization, particularly when combined with studies of the phonon sideband of PL.