  The charge dynamics of hydrogen-like centers formed by the implantation of
energetic (4 MeV) muons in semi-insulating GaAs have been studied by muon spin
resonance in electric fields. The results point to the significant role of deep
hole traps in the compensation mechanism of GaAs. Electric-field-enhanced
neutralization of deep electron and hole traps by muon-track-induced hot
carriers results to an increase of the non-equilibrium carrier life-times. As a
consequence, the muonium ($\mu^+ + e^-$) center at the tetrahedral As site can
capture the track's holes and therefore behaves like a donor.
