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 po- laron 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 Fröhlich coupling constant (α=0.068). The effects of uncertainties in the measured values of the dielectric constants (thus the value of α) are studied in the calculation, and the implication of these results for similar studies in GaAs/AlxGa1-xAs quantum wells is discussed.