Using noble gas argon as a diluent of SiH4 in RF glow discharge, undoped muc-Si:H thin films have been developed at a low power density of 30 mW/cm(2). It has been found that the gas pressure is a critical factor for the growth of muc-Si:H films. Undoped muc-Si:H films having sigma(D) similar to 10(-6) S/cm and DeltaE < 0.57 eV have been obtained at and above a critical pressure of 0.8 Torr. When the RF power density is increased to 90 mW/cm(2), a more crystalline as well as highly conducting (sigma(D) similar to 10(-4) S/cm) muc-Si:H film has been achieved at a deposition rate of 30 Angstrom/min, which is much higher than that attained from H-2-diluted SiH4 plasma, by conventional approach. The crystallinity of the films has been identified by the sharp Raman peak at similar to520 cm(-1) and a large number of micrograms in the TEM micrographs. The metastable state of Ar, denoted as Ar*, plays the crucial role in inducing microcrystallisation by transferring its de-excitation energy at the surface of the growing film. A mechanism has been proposed to explain the dependence of the formation of muc-Si:H film on the working gas pressure in the plasma. (C) 2003 Elsevier B.V. All rights reserved.