Approximate theory of temperature coefficient of resistivity of amorphous semiconductors

In this paper, we develop an approximate theory of the temperature coefficient of resistivity (TCR) and conductivity based upon the recently proposed microscopic response method. By introducing suitable approximations for the lattice dynamics, localized and extended electronic states, we produce explicit forms for the conductivity and TCR, which depend on easily accessible material parameters. The theory is in reasonable agreement with experiments on a-Si:H and a-Ge:H. A long-standing puzzle, a ``kink'' in the experimental log₁₀σ versus 1/T curve, is predicted by the theory and attributed to localized to extended transitions, which have not been properly handled in earlier theories.