Zinc sulfide [ZnS] thin films were deposited on glass substrates using radio frequency magnetron sputtering. The substrate temperature was varied in the range of 100°C to 400°C. The structural and optical properties of ZnS thin films were characterized with X-ray diffraction [XRD], field emission scanning electron microscopy [FESEM], energy dispersive analysis of X-rays and UV-visible transmission spectra. The XRD analyses indicate that ZnS films have zinc blende structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM data also reveal that the films have nano-size grains with a grain size of approximately 69 nm. The films grown at 350°C exhibit a relatively high transmittance of 80% in the visible region, with an energy band gap of 3.79 eV. These results show that ZnS films are suitable for use as the buffer layer of the Cu(In, Ga)Se2 solar cells.
Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapor deposition method from a mixture of methane, silane, and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the diborane and phosphine levels on the deposition rate, optical band gap and conductivity were investigated. In the case of boron-doped films, there is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were all amorphous and the band gap decreases as the diborane level is increased, whereas films deposited at a high microwave power of 800 W at low diborane levels are highly conductive and contain the silicon microcrystalline phase. These films become amorphous as the diborane level is increased, while the optical band gap remains relatively unaffected throughout the entire range of diborane levels investigated. In the case of phosphorus-doped films, Raman scattering analysis showed that the deposition conditions strongly influence the structural, optical, and electrical properties of the SiC:H films. Unlike boron doping, doping with phosphorus can have the effect of increasing the silicon microcrystalline phase in the SiC:H films, which were prepared at low (150 W) and high (600 W) microwave powers. Films prepared at high microwave power showed only small variations in the optical band gap, suggesting that good phosphorus doping efficiency can be achieved in films that contain the silicon microcrystalline phase (mc-SiC:H).
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