Post-growth annealing effects in compensated μc-Si:H samples

Abstract

In this work we study the effect of low temperature annealing on the transport properties of μc-Si:H. We performed post-growth annealing on a series of micro-doped μc-Si:H samples having different degrees of compensation, extending from n-type to p-type character. The samples were isothermally annealed at 423 K, 10 K below the deposition temperature. An increase of up to four orders of magnitude was observed in the dark conductivity ( σ dk) for the low temperature region. Simultaneously, the activation energy ( E a) of the dark conductivity changes depending on the doping level and the annealing time. Absorption coefficient and density of states measurements have been done for different annealing stages by using the constant photocurrent method and the modulated photocurrent technique, respectively. The density of defects in the midgap region increases during the annealing while the band tails remain unaffected. The σ dk and E a behavior can be interpreted in terms of a shift of the Fermi level towards the valence band. A model based in doping activation is proposed in order to explain this behavior.