Magneto-optical Investigation of the Free-Exciton Reflectance from High-Purity Epitaxial GaAs

The free-exciton reflectance structure at 1.5149 ± 0.0001 eV (2 K, zero field) in GaAs has been studied with polarized light in magnetic fields up to $H\approx 250$ kG. Large shifts, up to six times the exciton binding energy, and complex splittings of the eightfold-degenerate exciton ground state have been observed. These effects have been analyzed with a simple hydrogenic model as well as with a low-field perturbation model that includes the anisotropy and degeneracy of the zinc-blende valence band at $k=0\mathrm{}$. The shifts are satisfactorily accounted for over the whole range, whereas only qualitative agreement between the predicted and observed splitting pattern is achieved. Reasons for this discrepancy are discussed.