Field-Dependent Central-Cell Corrections in GaAs by Laser Spectroscopy

We report the first definite observations of the magnetic field dependence of centralcell corrections in shallow donors. Exploiting the extreme resolution inherent in magnetospectroscopy employing infrared gas laser sources, we have observed previously unresolved transitions arising from four distinct "hydrogenic" donor species occurring in high-purity epitaxial GaAs. We show that the species-dependent differences in transition energies are directly proportional to the probability of finding an electron at the donor site to which it is loosely bound. This probability increases with increasing magnetic field because of magnetic squeezing of the wave function of the bound electron.