Self-trapped single-particle excitations in equilibrium and photoconductivity in glassy semiconductors

A consistent theory of photoconductivity in glassy semiconductors is presented, which is related to negative-U centers associated with soft atomic configurations. Properties of localized single-particle excitations related to negative-U centers and their contributions to both equilibrium phenomena (e.g., thermally induced paramagnetism) and weakly nonequilibrium ones (photoconductivity, etc.) are studied. An analysis of the energy dependence of cross sections of carrier trapping and related effects is given. A new recombination channel associated with the single-particle excitations is described. Manifestations of both continuum properties and effective discrete energy-level features of the mobility-gap spectrum in glassy semiconductors are considered.