Photo-Hall-effect measurements of ionized impurity scattering in GaAs

We use the photo-Hall effect in the ionized-impurity scattering conduction regime in GaAs to determine the effects of illumination on the carrier mobility $\mu$. By employing low-level ac light pulses we are able to investigate the quasistatic case and can isolate those effects due to illumination. We find that the $\mu$ enhancement observed upon illumination may be understood in terms of: (i) the screening of ionized donors by electrons, (ii) carrier freeze out in the Brooks-Herring formalism, and (iii) photoinduced carrier heating.