In the field of photovoltaics, semiconductors of the III-V group such as GaAs and InP have been considered as the most efficient absorber materials due to their direct energy band gap and high mobility. In these compounds, arsenic and phosphorus are highly toxic and expensive. In this work we present systematic preparation of low cost SnS thin films and characterize these films to test their suitability for photovoltaic applications. We have observed that the films (with thickness ≅0.5μm) grown at the substrate temperature of 275°C exhibit a low resistive single SnS phase and have a direct optical band gap of 1.35eV with an absorption coefficient of ∼105cm−1. SnS films could be alternative semiconductor materials as absorbers for the fabrication of photovoltaic devices.

SnS films with different thicknesses have been deposited on glass substrates at a constant substrate temperature of 300°C . The physical properties of the films were investigated using energy dispersive analysis of X-rays, X-ray diffraction, scanning electron microscopy, atomic force microscopy, van der Pauw method, and Fourier transform infrared spectroscopy measurements at room temperature. The deposited films exhibit only SnS phase with different orientations. We show that the electrical resistivity, activation energy, and optical bandgap of the films depend strongly on the preferred orientation of the SnS films. The electrical resistivity of films decreased with the increase of film thickness. The optical and electrical data of the SnS film are well interpreted with the composition, crystal, and surface structure data.

Amorphous Ge2Sb2Te5 (GST) alloy, upon heating crystallize to a metastable NaCl structure around 150°C and then to a stable hexagonal structure at high temperatures (≥250°C). It has been generally understood that the phase change takes place between amorphous and the metastable NaCl structure and not between the amorphous and the stable hexagonal phase. In the present work, it is observed that the thermally evaporated (GST)1-xSex thin films (0 ≤ x ≤ 0.50) crystallize directly to the stable hexagonal structure for x ≥ 0.10, when annealed at temperatures ≥ 150°C. The intermediate NaCl structure has been observed only for x < 0.10. Chemically ordered network of GST is largely modified for x ≥ 0.10. Resistance, thermal stability and threshold voltage of the films are found to increase with the increase of Se. The contrast in electrical resistivity between the amorphous and crystalline phases is about 6 orders of magnitude. The increase in Se shifts the absorption edge to lower wavelength and the band gap widens from 0.63 to 1.05 eV. Higher resistance ratio, higher crystallization temperature, direct transition to the stable phase indicate that (GST)1-xSex films are better candidates for phase change memory applications.

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The effect of annealing on the composition, crystal structure, surface features and electro-optical properties of tin mono-sulfide (SnS) films, deposited by thermal evaporation at 300 • C, has been studied. Elemental analysis of the films shows sulfur deficiency, which increases at higher annealing temperatures (T a). The SnS structure in the as-deposited and annealed films remains orthorhombic. With an increase in T a , the grain size and the surface roughness are reduced. The electrical resistivity also decreases with increasing T a. The variation of activation energy and optical parameters with T a has been explained by taking into account the degree of preferred orientation of the grains. The films annealed at 100 • C show some unusual features compared to those annealed at other temperatures.

The development of high-quality tin monosulphide (SnS) layers is one of the crucial tasks in the fabrication of efficient SnSbased optoelectronic devices. Reduction of strain between film and the substrate by using an appropriate lattice-matched (LM) substrate is a new attempt for the growth of high-quality layers. In this view, the SnS films were deposited on LM Al substrate using the thermal evaporation technique with a low rate of evaporation. The as-grown SnS films were characterized using appropriate techniques and the obtained results are discussed by comparing them with the properties of SnS films grown on amorphous substrate under the same conditions. From structural analysis of the films, it is noticed that the SnS films deposited on amorphous substrate have crystallites that were oriented along different directions. However, the SnS crystallites grown on Al substrate exhibited epitaxial growth along the [101] direction. Photoluminescence (PL) and Raman studies reveal that the films grown on Al substrate have better optical properties than those of the films grown on amorphous substrates.

Ag-doped SnS films have been grown with a thickness of ϳ0.5 m by thermal evaporation technique on Coring 7059 glass substrates at a substrate temperature of 275°C. The effects of doping on the physical properties of the films have been investigated. The physical characteristics of the films are discussed and correlated to the microstructural and electro-optical properties. Electrooptical studies show that undoped SnS films have an electrical resistivity and optical bandgap of 35.6 ⍀ cm and 1.35 eV at room temperature. With the increase of Ag dopant concentration, the resistivity of the SnS layers initially decreased, reached a minimum value of 6.98 ⍀ cm at 15 atom % of Ag and again increased thereafter. However, optical bandgap ͑E g ͒ of the films decreased nonlinearly with increase of Ag percentage. An empirical formula E g = 1.345-0.0014 X + 5.952 ϫ 10 −5 X 2 , which describes the energy gap as a function of the film composition, has been derived. The doping effect on the surface structure of SnS films was also studied.