For instance, use is made of hydrocarbons such as methane (CH4), ethane (C2 H6), propane (C3 H8), ethylene (C2 H4) and the like, tetra fluoro methane (CF4), tetra methylsilane ((CH3)4 Si), tetre ethylsilane ((C2 H5)4 Si) and the like for carbons to be contained into the semiconductor layer.