Optical, structural evolution and surface morphology studies of hydrogenated silicon films synthesized by rf-magnetron sputtering: Effects of pressure and radio frequency power at low temperature

In the present work, three series of hydrogenated silicon thin films were prepared by radiofrequency magnetron sputtering method at low temperature, various deposition pressures (2, 4, 6 Pa) and different rf powers (200, 300, 400, 500 W) while all the other plasma parameters were fixed. The deposited films were characterized using atomic force microscopy (AFM), Fourier transform infrared (FTIR), UV-vis-NIR spectroscopy, Raman spectroscopy, X-ray diffraction (XRD) and DC electrical conductivity. The results show that rf power and pressure play an important role on optical band gap, the content of hydrogen, crystalline volume fraction, grain size and the surface roughness. The samples prepared at 6 Pa show the phase transition from amorphous, polymorphous to microcrystalline with increasing rf power. This transition is accompanied by an increase of the crystalline volume fraction and grain size, where hydrogen rich amorphous matrix enhances the crystallization. The variation of the optical band gap with the rf power was found to be dependent on the structure and hydrogen content. We conclude that increasing rf power favors the growth of microcrystalline films where the substrate was reheated by a high energy ions bombardment. The activation energy decreases linearly with increasing crystalline volume fraction.