Muonium in ultra-pure and Si-doped germanium

The influence of the isoelectronic impurity silicon ([Si]=1012−1018 cm−3) on the spin precession signals of positive muons in ultra-pure germanium crystals is investigated between 5 and 340 K in transverse magnetic fields of 0.5 to 27.5 mT. Normal (“isotropic”) muonium atoms Mu are formed in all samples with about the same probability (≈ 0.7). Down to quite low temperatures (20 K) Mu is found to diffuse very rapidly through the Ge matrix and to become ionized by interaction with the Si atoms. Another ionization process, presumably due to the screening of theμ+ by the increasing number of free charge carriers, sets in at about 180 K.