Field-dependent negative-U model and switching in chalcogenide glasses

Abstract

Using the Anderson negative-U model, with harmonically bound ionic charges, one finds that the electric dipoles of singly (D₀) and doubly (D_-) occupied dangling bonds can be streched by a strong electric field. The D₀ and D_- energies become field-dependent, with the splitting E₀(F_-)-E_-(F) vanishing at a critical field F_c when D₀ becomes more stable. Assuming that Zener tunneling to extended states occurs only from singly occupied states, but not from D_- states, a qualitative picture for Ovshinsky switching follows: there will be a jump in the D₀ occupation and hence in the carrier concentration at F = F_c. Field magnitudes and delay times are estimated. Memory switching is also discussed.