The microscopic study of a single hydrogen-like impurity in   semi-insulating GaAs
  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. 
D.G. Eshchenko, V.G. Storchak, S.P. Cottrell, E. Morenzoni