A consistent theory for the 2-band self-trapping of electrons (holes) in semiconductors was presented. Here, negative-U centers in the inter-band (mobility) gap were formed as singlet electron (hole) pairs which were self-trapped in atomic soft configurations. Both the configurational softness and the hybridization of the bare single-electron state with extended band states were considered to be essential for the formation of the self-trapped states and negative-U centers. Hybridization markedly changed the appropriate soft configurations and introduced additional anharmonic features into the related atomic dynamics. Suggested examples were mobility-gap states and negative-U centers, and their related atomic dynamics, in glassy semiconductors.

M.I.Klinger, S.N.Taraskin: Physical Review B, 1995, 52[4], 2557-73