Magnetopolaron effect on shallow donors in GaAs.

Low-temperature experimental measurements and variational calculations of the transition energies of shallow donor (Si) impurities in bulk GaAs as a function of magnetic field throughout the resonant polaron region are reported. Far-infrared photoconductivity spectra in magnetic fields up to 23.5 T show several anti-level-crossing processes at energies above the LO-phonon energy, clearly demonstrating the resonant interactions between GaAs LO phonons and impurity-bound electrons involving several excited impurity states. Very good agreement is obtained between experiment and calculated transition energies throughout the resonant region with the accepted value of the Frohlich coupling constant (α=0.068)