Polymorphous silicon (pm-Si:H) is a nanostructured material that has attracted much attention due to its unique structure and electronic properties that make it an excellent alternative to a-Si:H for photovoltaic applications. In this study we present the effects of the plasma excitation frequency (13.56, 27.12 and 40.68 MHz) and of dopants on the formation of clusters in the plasma, and correlate them to the optical and electronic properties of the films. While previous studies have focused on films incorporating crystallites and clusters with sizes of 1-3 nm, the analysis of the roughness by in situ spectroscopic ellipsometry suggests that more ordered films result from the incorporation of agglomerates with sizes up to 10 nm. Moreover, the increase of the excitation frequency does not enhance the deposition rate, it only shifts the maximum value of deposition rate to the lower deposition pressure. (C) 2003 Elsevier B.V. All rights reserved.