Transient photoconductivity, density of tail states and doping effect in amorphous silicon

The Transient Photoconductivity (TPC) is studied in the pre-recombination t ime range on the basis of a Multiple Trapping (KIT) model which uses a tran sient occupation function to account for simultaneous interactions of all t he tail states with the conduction band. A direct inversion method for the extraction of the Density Of States (DOS) from the TPC data in amorphous se miconductors is derived. Application of this transient spectroscopy to n-ty pe a-Si:H results in a very narrow band tail (tail width of 14 meV) startin g around 0.16 eV below the mobility edge and leading to low DOS. This findi ng is in favour of the defect pool concept, and involves some doping effect s at the donor level. (C) 1999 Published by Elsevier Science Ltd. All right s reserved.