In this study, we report the morphological and structural properties of amorphous and nanocrystalline Si thin films deposited by inductively coupled plasma-assisted chemical vapor deposition (ICP-CVD) technique at low substrate temperatures using H-2 diluted SiH4 as the source gas. We demonstrated that changing the total deposition pressure across a broad range alters the film properties. The film grew in a columnar fashion, and its topography was rough at nanoscale as identified by high resolution Transmission Electron Microscopy (TEM), independent of its amorphous or crystalline nature. Further investigation of the structure revealed that the columns consisted of structures resembling highly porous cauliflower. Additionally, these cauliflower-like Si nanostructures oxidized gradually and extremely uniform throughout the film when exposed to air due to their highly porous nature. We have explained the formation of these structural properties using ballistic growth theory and reactive radicals' effect. (C) 2014 Elsevier Ltd. All rights reserved.