Hydrogenated Nanocrystalline Silicon Thin Films Prepared by Hot-Wire Method with Varied Process Pressure

Hydrogenated nanocrystalline silicon films were prepared by hot-wire method at low substrate temperature (200∘C) without hydrogen dilution of silane (SiH4). A variety of techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and UV-visible (UV-Vis) spectroscopy, were used to characterize these films for structural and optical properties. Films are grown at reasonably high deposition rates (>15 Å/s), which are very much appreciated for the fabrication of cost effective devices. Different crystalline fractions (from 2.5% to 63%) and crystallite size (3.6–6.0 nm) can be achieved by controlling the process pressure. It is observed that with increase in process pressure, the hydrogen bonding in the films shifts from Si–H to Si–H2 and (Si–H2)n complexes. The band gaps of the films are found in the range 1.83–2.11 eV, whereas the hydrogen content remains <9 at.% over the entire range of process pressure studied. The ease of depositing films with tunable band gap is useful for fabrication of tandem solar cells. A correlation between structural and optical properties has been found and discussed in detail

X-ray photoelectron spectroscopic studies of oxygen chemisorption on thick films of photoconducting cadmium sulfide

X-ray photoelectron spectroscopic studies of highly photosensitive thick films of cadmium sulphide have been carried out which reveal the appearance of a complex triplet structure (S2p) spread over about 20 eV with peaks centered at binding energy values of 162.6, 172.8, and 179.7 eV. Using the available literature data, the S2p peak at 162.6 eV is interpreted to originate from S−− ions, the one at 172.8 eV from the SO−−4− like species and that at 179.7 eV from SO2−like species, the latter two being formed on the surface due to the preferential bonding of chemisorbed oxygen with sulphur. After thermal desorption, the films exhibit no photosensitivity and there is a substantial reduction in the intensities of 172.8-and 179.7-eV peaks. A close link between the existence of SO−− 4 and SO2 (adsorbed) species and photoconductivity is clearly manifested

Studies on thick films of photoconducting cadmium sulphide

Highly photosensitive films of CdS have been prepared using the thick film technique. The films obtained from the composition containing CdS-100, CdCl2−10 and CuCl2−0·05 parts by weight (reacted at 500° C) are found to give the best photosensitivity on firing at 600° C. The ratio of light to dark current ~108-109 which is considerably higher than what is reported for thin films, single crystals and sintered layers. A strong chemisorption of oxygen is found to be responsible for high photosensitivity. The spectral response for doped CdS film is similar to that obtained for thin films, single crystals and sintered layers and also shows a red shift with increasing Cu concentration. However, the undoped CdS has a broad spectral response at room temperature ranging fromλ=550 to 690 nm; unlike the thin films and single crystals which give a sharp peak atλ=510 to 520 nm. A probable explanation has been suggested for this type of behaviour