The absorption coefficient of the material should be high, about 104–106 cm−1. Materials with higher absorption coefficient can easily absorb photons and excite electrons into the conduction band. For thin film solar cell, we need a thin absorption layer with good absorption coefficient. But, the absorption coefficient of Si layer is low in the visible region of solar radiation and therefore absorption layer should be more than 1 µm thick. Thus, the film deposition rate should be high in order to make solar cell commercially viable. For this purpose high power and very high plasma excitation frequency are used [6]. The optical absorption in indirect band gap semiconductor is lower than direct band gap semiconductor. The absorption coefficient can be enhanced at nanodimension [11].