Spectral and thermodynamic properties of electrons in mobility gap states of covalent glasses

Spectral and thermodynamic properties of electrons (holes) in covalent semiconducting glasses are considered in which self-trapping of electron (hole) pairs is realized with negative effective correlation energy U^?. Unlike the Anderson model, electron (hole) pairing is restricted to a small part of the glass bonds. Ranges of the U^? values are found in which either pair effects (suppression of paramagnetism etc.) or single-particle effects predominate; the concentration of the pair states and of the occupied ones can roughly be estimated and can be fairly high. The problem of the coexistence of the Fermi level pinning and effective diamagnetism in glasses is discussed. Some related effects are briefly considered.