SnSe thin films of thickness 180 nm have been deposited on glass substrates by reactive evaporation at an optimized substrate temperature of 523 ± 5 K and pressure of 10−5 mbar. The as-prepared SnSe thin films are characterized for their structural, optical and electrical properties by various experimental techniques. The p-type conductivity, near-optimum direct band gap, high absorption coefficient and good photosensitivity of the SnSe thin film indicate its suitability for photovoltaic applications. The optical constants, loss factor, quality factor and optical conductivity of the films are evaluated. The results of Hall and thermoelectric power measurements are correlated to determine the density of states, Fermi energy and effective mass of carriers and are obtained as 2.8 × 1017 cm−3, 0.03 eV and 0.05m0 respectively. The high Seebeck coefficient ≈ 7863 μV/K, reasonably good power factor ≈ 7.2 × 10−4 W/(m·K2) and thermoelectric figure of merit ≈ 1.2 observed at 42 K suggests that, on further work, the prepared SnSe thin films can also be considered as a possible candidate for cryogenic thermoelectric applications.
Polycrystalline thin films of the ordered vacancy compound AgGa 3 Se 5 were prepared by a multisource vacuum coevaporation technique at a substrate temperature of 623 K. X-ray diffraction and atomic force microscopy in conjunction with energy-dispersive analysis of X-rays and X-ray photoelectron spectroscopy were used for the structural, morphological, and compositional characterization. The distortion parameter and the anion displacement deduced from the X-ray diffraction data using the CTB plus h ¼ h tet rule were used for obtaining the anion-cation bond lengths. The compound manifested a slight increase in the nonideal anion displacement compared to AgGaSe 2 . The films with ternary chalcopyrite structure were found to possess an enhanced direct allowed bandgap of $1.8 eV compared to that in AgGaSe 2 indicative of the slightly reduced p-d interband repulsion due to the periodic introduction of silver vacancies. The electrical resistivity was assessed to be of the order of 10 À1 V m with n-type conductivity and the films exhibited good photosensitivity. An unusual increase in Seebeck coefficient was manifested in the low-temperature range 4-330 K with negligible phonon drag toward the very low and room temperature regime.
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