Far-Infrared Donor Absorption and Photoconductivity in Epitaxialn-Type GaAs

Donor-state absorption and photoconductivity spectra of $n$-type epitaxial GaAs layers with carrier concentrations in the range ${10}^{14}$-${10}^{16}$/${\mathrm{cm}}^3$ are reported. The essentially effective-mass-like behavior of the impurity spectra is confirmed, and ionization energies of 6.08, 5.81, 5.89, and 6.10±0.025 meV are reported for Ge, Si, Se, and S donors. The influence of impurity-banding upon the values of $E_D$ is considered. Central-cell corrections to donor ground-state energies are discussed.