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 (${\mathrm{Mu}}_{\mathit{T}}^0$), while it has relatively weak effect on the bond-center muonium (${\mathrm{Mu}}_{\mathrm{BC}}^0$). In metallic GaAs:Si, the highly mobile ${\mathrm{Mu}}_{\mathit{T}}^0$ center observed in nonmetallic GaAs is replaced by a charged species (probably ${\mathrm{Mu}}^{\mathrm{-}}$) which shows a diffusion rate at least ${10}^{\mathrm{-}2}$ times smaller than the ${\mathrm{Mu}}_{\mathit{T}}^0$ center. The ${\mathrm{Mu}}_{\mathrm{BC}}^0$ center is metastable and its transition to ${\mathrm{Mu}}_{\mathit{T}}^0$ or ${\mathrm{Mu}}^{\mathrm{-}}$ centers (depending on doping concentration) is seen in the 50–150-K range. The current results also suggest that the ${\mathrm{Mu}}_{\mathit{T}}^0$ state undergoes fast spin-exchange interaction with conductive carriers prior to the transition ${\mathrm{Mu}}_{\mathit{T}}^0$→${\mathrm{Mu}}^{\mathrm{-}}$.