ATOMIC TUNNELING STATES AND NEGATIVE-U ELECTROK PAIRS IN AMORPHOUS SEMICONDUCTORS

The relation between atomic tunneling states (ATS) and negative-U electron pairs in amorphous semiconductors is the oretically investigated in a simple model. By considering the interaction of ATS with the electrons of dangling bonds,we can not only derive negative-U electron pairs, but also explain the different properties between chalcogenide glassy semiconductors and tetrahedrally bonded amorphous semiconductors in a nature way. The connection of the density of the states of ATS with the electronic states of dangling bonds is also discussed, and our results can qualitatively account for the recent experiment of Fox et al. In addition, the urbach rule in chalcogenide glassy semiconductors is derived.