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Highly photoconducting (ημτ) films of a-SiGe: H with very low defect densities have been produced by a plasma-enhanced chemical vapour deposition technique under low flow rate (2·5 sccm) of source gases (silane and germane) and hydrogen dilution. The defect states have been characterized by photothermal deflection spectroscopy, the constant photocurrent method dual-beam photoconductivity and electron spin resonance. A low deposition rate is necessary to obtain high-quality alloy materials with comparatively high band gaps, i.e., 1·7eV>Eg> 1·5 eV, as manifested by a small disorder (lower Urbach parameter E0) and defect density, ND (mainly reduced Ge dangling-bond density), whereas additional hydrogen dilution of the source gases is necessary to reduce ND in the low band-gap region. Hydrogen dilution improves homogeneity throughout the band-gap region with a corresponding decrease of E0 values which has no correlation with the reduction of ND. Studies of the temperature dependence of the photoconductivity and infrared quenching reveal that the large ημτ values in the optimized materials are not due to sensitization effects, but because of extremely low dangling-bond densities. This is supported by light-induced electron spin resonance studies where a significant increase in the number of carriers in the band tails has been observed in the optimized materials. The experimental results on the deposition rate and hydrogen dilution dependence of electronic and structural properties are consistent with a bulk thermal equilibration model.

In this paper we present a computer simulation study of ionic conductivity in solid polymeric electrolytes. The multiphase nature of the material is taken into account. The polymer is represented by a regular lattice whose sites represent either crystalline or amorphous regions with the charge carrier performing a random walk. Different waiting times are assigned to sites corresponding to the different phases. A random walk (RW) is used to calculate the conductivity through the Nernst-Einstein relation. Our walk algorithm takes into account the reorganization of the different phases over time scales comparable to time scales for the conduction process. This is a characteristic feature of the polymer network. The qualitative nature of the variation of conductivity with salt concentration agrees with the experimental values for PEO-NH4I and PEO-NH4SCN. The average jump distance estimated from our work is consistent with the reported bond lengths for such polymers.