MU-SR STUDIES IN HEAVILY-DOPED GAAS

Transverse-field (TF) and longitudinal-field (LF) mu+SR measurements h ave been made on conducting GaAs:Si (n-type almost-equal-to 10(18) cm- 3) and GaAs:Zn (p-type almost-equal-to 10(19) cm-3) from 20 mK to 200 K. At low temperatures in GaAs:Si, the frequency spectra show a large diamagnetic signal as well as broad lines due to bond-centered muonium (Mu(BC)). This broadening is attributed to spin exchange interactions with charge carriers in impurity bands. Only the diamagnetic signal i s observed in GaAs:Zn. The field dependence of the TF diamagnetic rela xation rate at 5 K can be explained by the combined electric quadrupol ar and Zeeman interaction between the muon and the surrounding nuclei and the temperature scan at TF=1.5 T indicates that the mechanisms res ponsible for the broadening are temperature independent. The candidate s for the diamagnetic species are discussed in view of these results.