Growth of crystalline silicon by a seed layer approach using plasma enhanced chemical vapor deposition

Different processes are used to improve the deposition of a nanocrystalline silicon layer to enhance optical absorption in different devices. The difficulty encountered lies in the reproducibility and cost of the process. In the present study, we have investigated the effect of a crystalline seed layer on the structural properties of a subsequent hydrogenated silicon (Si:H) layer (top layer). Structural properties of deposited films were investigated by absorption and Raman spectroscopy, grazing incidence X-ray diffraction measurements and spectroscopic ellipsometry. They show that using the seed layer approach promotes the structural evolution of the subsequent layer by improving its size and fraction of crystallites. UV–visible reflectance spectra simulations using Bruggeman effective medium approximation were used in order to investigate the composition evolution of the studied samples. They predict that the optical model of the elaborated layers consists of (i) the crystalline substrate (ii) the incubation layer (a mixture of amorphous silicon and voids) (iii) the bulk crystalline layer (a mixture of amorphous silicon, crystalline silicon and voids) and finally (iv) the surface layer. The incubation layer observed at the beginning of growth of the subsequent layer is absent in the optical model in the presence of the seed layer or it may be very thin in thickness, so that it has not been presented in the optical model. The optical model shows also an increase of void fraction in the top layer in the presence of the seed layer; this has been linked to the increase of crystallite size. It is noted also that the top layer is rougher in the presence of the seed layer and this has been attributed to the presence of larger silicon crystallites on its surface. Such deposition process can be used to enhance crystalline phase in absorber layer for optoelectronic devices.