Donor metastable states and resonant electron-phonon interaction in n-GaAs

Far-infrared photoconductivity measurements on n-GaAs using a far-infrared laser and a Fourier-transform spectrometer are reported. They extend previous measurements to higher magnetic fields (14 T) and higher laser energies (330 cm-1) and, in particular, give results in those regions of the spectra where resonant polaron effects on transitions to metastable states are clearly present. To describe the field dependence of the transition energies, a new variational-type approach for the calculation of the energies of the metastable states has been developed. As such an approach yields analytical expressions for the wave functions, the effects of resonant polaron interactions on the transition energies can be calculated. Experimental and theoretical transition energies are compared for the more important transitions to metastable states, including resonant polaron effects, and very good agreement is obtained even though the theoretical model is very simple.