HYPERFINE INTERACTIONS FOR IMPURITIES IN SEMICONDUCTORS

Recently, extensive electronic structure calculations have been performed in order to elucidate several interesting problems associated with the transition-element impurities and a positive muon in semiconductors. Possibility of multiple charge states, high-spin state versus low-spin state, quenching of orbital angular momentum, reduction in the impurity hyperfine field, impurity dependence as well as site dependence of super-hyperfine field, and a peculiar hyperfine coupling constants for anomalous muonium are some of the problems treated so far. Theoretical works on these problems are reviewed from a viewpoint of the hyperfine interactions, with emphasis on the following two aspects. First, the hybridization between the impurity states and the host states is a key concept in all of the above problems. Second, the hyperfine field of the Fermi contact origin is analyzed in terms of two basic mechanisms, the population polarization and the exchange polarization.