The objective of our work was the development of an alternative doping method of amorphous and microcrystalline silicon for solar cell applications. n-type amorphous silicon films were prepared from gas mixtures containing the dopant vapor trimethylphosphine (TMP, P(CH3)(3)) diluted in hydrogen-instead of the well-known phosphorus source phosphine (PH3)-silane and hydrogen. Different plasma sources were used-operating at 13.56, 27.12 MHz (parallel plate capacitive type system) and 163 MHz (VHF resonance plasma source). For all the investigated frequencies and plasma sources a dark conductivity maximum level (at room temperature) higher than 3 X 10(-3) Omega(-1) cm(-1) could be reached, with dopant levels (TMP/silane concentration) in the range of 10(-3)-10(-2). The sharp decrease of the dark conductivity for higher dopant concentrations (which is characteristic for the hydrocarbon-based phosphorus sources due to the formation of silicon carbide within the silicon structure) was not detected up to dopant levels of 4 X 10(-2).