ELECTRONIC-STRUCTURE OF ANOMALOUS MUONIUM IN GAP AND GAAS

The nuclear hyperfine structure of anomalous muonium in GaP has been r esolved using muon level-crossing resonance. We find that 43% of the u npaired electron spin density resides on the nearest-neighbor Ga and 3 5% on the nearest-neighbor P on the [111] axis of symmetry. The s and p character of the unpaired spin density indicates that the Ga and P a re displaced 0.23 and 0.54 angstrom away from the bond center. The now complete set of measured muon and nearest-neighbor nuclear hyperfine parameters for anomalous muonium in GaP and GaAs allows a detailed com parison of the two compounds, showing that the distribution of spin de nsity among the group-III and group-V nearest neighbors in GaP is almo st exactly the opposite of that in GaAs. This is contrary to what one would expect from a simple model of anomalous muonium in compound semi conductors involving an account of bonding characteristics.