CHARGE-STATE AND DIFFUSIVITY OF MUONIUM IN N-TYPE GAAS

The presence of Si donors in GaAs exerts a strong influence on the charge state and diffusion of muonium at the tetrahedral interstitial site (Mu(T)0), while it has relatively weak effect on the bond-center muonium (Mu(BC)0). In metallic GaAs:Si, the highly mobile Mu(T)0 center observed in nonmetallic GaAs is replaced by a charged species (probably Mu-) which shows a diffusion rate at least 10(-2) times smaller than the Mu(T)0 center. The Mu(BC)0 center is metastable and its transition to Mu(T)0 or Mu- centers (depending on doping concentration) is seen in the 50-150-K range. The current results also suggest that the Mu(T)0 state undergoes fast spin-exchange interaction with conductive carriers prior to the transition Mu(T)0-->Mu-.