Saddle-point excitons and intraband (Γ-Π) mixing in strained-layer superlattices

Magneto-optical studies have been conducted on two Inₓ{Ga}_{1{{-}}x}$As/GaAs superlattices to investigate excitonic transitions at the saddle points formed at ${q}z$={π}/d of the superlattice miniband structure. We report on a direct observation of both the E1({Π})-HH1({Π}) saddle-point exciton and the indirect E1({Γ})-HH1({Π}) excitonic resonance in both perpendicular and parallel magnetic fields, with both features showing perpendicular field-induced ({Γ}-{Π}) mixing in the separate carrier minibands. Theoretical calculations demonstrate highly field- and wave-vector-dependent valence-band g factors, which, because of the small valence-band widths, lead to the inversion of the mⱼ=+3/2 E-qz dispersion curves at high perpendicular fields. The unusual behavior of the light-hole transitions indicates a large degree of in-plane mixing of the heavy- and light-hole states, which would appear to be closely linked to the observed wave-vector mixing and complex g factors.