The effect of microwave power density on the structure properties of microcrystalline silicon films (mu c-Si films) deposited by high-density (> 10(12) cm(-3)) low-ion-energy microwave plasma at 400 degrees C substrate temperature has been investigated with X-ray diffraction, Raman spectra and atomic force microscopy. The mu c-Si films are deposited under conditions of depletion of silane in order to avoid the combined effect of deposition rate and plasma bombardment. The experimental results indicate that the reduction of the power density causes a shoulder to fortri in the Raman spectra and the microstructure of the films changes from dominant (110) to random. Based on the experimental results, it is deduced that a large quantity of ions impinging on the growth surface can prevent a polymerization reaction among the silane radicals and promote the formation of the (110) preferred orientation mu c-Si film. The present results are successfully explained in terms of the mechanism of collision of ions with the precursor adsorbed on the growth surface. (c) 2005 Elsevier B.V. All rights reserved.