Photoconductivity studies of n-type hydrogenated amorphous silicon and microcrystalline silicon

Abstract

Photoconductivity techniques serve as useful tools for the characterization of amorphous and microcrystalline silicon. From the link between the majority carrier mobility–lifetime product from steady-state photoconductivity and the position of the Fermi level, useful insight can be gained when comparing sample properties. The temperature dependence of the minority carrier mobility–lifetime product implies that the band-tail region of the density-of-states (DOS) is steeper in microcrystalline silicon than in amorphous silicon. Transient and modulated photoconductivity determine the DOS in the upper half of the band gap, for which we find an exponential variation. We indicate that the Fermi level or quasi-Fermi level impose limitations on the DOS extraction from the measured data. In samples in which the Fermi level is shifted towards the conduction band, the DOS calculation then yields values that are too low.