Preparation and characterization of Cu2ZnxFe1−xSnS4 thin ‎films deposited on intrinsic silicon substrates

International audienceThe present paper reports the study of the effect of zinc content in Cu2Zn1−xFexSnS4 thin films. To achieve this purpose, CZTS, CZ0.5F0.5TS and CZTS thin films were grown at room temperature via thermal evaporation on unheated silicon substrates, which was followed by sulfidation at 400 °C. Analysis by x-ray diffraction indicates the polycrystalline nature of the CZFTS films with a preferential orientation along the (112) plane with structural transition from stannite (x = 0) to kesterite (x = 1) as the zinc content increases. The elemental composition of all thin films was analyzed by the EDAX technique. Morphological patterns were also explored in order to better understand the evolution of grain size and thickness as a function of zinc content. Hall effect measurements showed that the highest conductivity was obtained for CZTS. Impedance spectroscopy (IS) was performed between 5 Hz and 13 MHz. The complex impedance plots of the different samples revealed a single semicircle, suggesting that the response comes from a single capacitive element consistent with the grains. This measurement (IS) confirmed the enhancement of the conduction mechanism with increasing x-fraction. Experimental data suggested that AC conductivity in thin films C(Z, F)TS is proportional to ωs (s < 1). This is consistent with the correlated barrier hopping (CBH) model

Effect of vacuum annealing on structural, morphological and optical properties of Sn

Sn2Sb2S5 thin films in thickness of 100–900 nm were deposited on unheated glass substrates using thermal evaporation method and annealed in vacuum at temperature of 200 °C for 2 h. X-ray diffraction spectra indicated that all the Sn2Sb2S5 samples are polycrystalline in nature having orthorhombic structure. The various structural parameters, such as, crystalline size, dislocation density, strain and texture coefficient were calculated and the surface morphology of the films was also analyzed. The optical constants, i.e., refractive index, absorption coefficient and optical band gap of the as-deposited and post-annealed films have been determined from the analysis of the transmittance and reflectance spectral data over the wavelength range 300–1800 nm. All the Sn2Sb2S5 thin films before and after annealing have relatively high absorption coefficient between 104 and 105 cm−1 in the visible spectral range. The optical band gap was found to decrease, from 1.72 to 1.5 eV for samples before annealing and from 172 to 1.46 eV for samples annealed in vacuum, with increasing films thickness in the 100–900 nm range

Optical characterization of Sb2S3 vacuum annealed films by UV–VIS–NIR spectroscopy and spectroscopic ellipsometry: Determining the refractive index and the optical constants

Using UV–VIS–NIR spectroscopy and spectroscopic ellipsometry (SE) techniques, we studied the optical characteristics of Sb2S3 thin films produced by a one-step thermal evaporation process and annealed for 2 h at various temperatures under vacuum atmosphere. The X-ray diffraction study shows that a structural transition from amorphous to polycrystalline nature occurred at vacuum annealing temperature of 200 °C. According to UV–VIS–NIR spectroscopic measurements, the Sb2S3 films showed a high absorption coefficient in the visible region (α > 104 cm−1) and a direct band gap energy that decreases from 2.00 eV to 1.63 eV as the annealing temperatures increase. Furthermore, we calculate the optical constants of the elaborated Sb2S3 films, such as refractive index n and extinction coefficient k, by fitting the ellipsometric measurements of the pseudo-refractive index and the pseudo-extinction coefficient . It was observed that the obtained values for n at 800 nm are 2.7, 2.9, 3.5, and 4.0 for as-deposited and annealed films, respectively, at 150, 200, and 250 °C. The dielectric properties were also determined using the Wemple DiDomenico (WDD) and Spitzer-Fan models.E. Gnenna acknowledges the Tunisian Ministry of Higher Education and Scientific Research for providing a two-month internship at the ICMAB-CSIC Institute (Barcelona-Spain) . N. Khemiri also thanks the Tunisian Ministry of Higher Education and Scientific Research for support through the PEJC Young Researchers Encouragement Program (Project code 19PEJC03-11) . We are thankful to M. Kong for the profilometer measurements. M.I.A. thanks the Spanish Ministry (MICINN) for support through Grant CEX2019- 000917-S (FUNFUTURE) and the Catalan agency AGAUR for Grant 2017-SGR-00488. The Scientific and Technical Services of ICMAB are gratefully acknowledged for AFM and SEM measurements.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Effect of vacuum annealing on the properties of one step thermally evaporated Sb

Sb2S3 films were deposited on unheated glass substrates by thermal evaporation and annealed under vacuum atmosphere for 2 hours at different temperatures. Different characterization techniques were used to better understand the behavior of the Sb2S3 material. XRD and Raman spectroscopy confirmed the formation of pure Sb2S3 powder with orthorhombic lattices. The effect of vacuum annealing on the properties of the films was studied. XRD analysis revealed that as-deposited and annealed films at 150 °C were amorphous in nature whereas those annealed at T ≥ 200 °C were polycrystalline. The crystallite size of the films showed a decrease from 75.8 to 62.9 nm with the increase of the annealing temperature from 200 to 250 °C. The Raman showed several peaks corresponding to the stibnite Sb2S3 phase. The surface morphology of the films was examined by AFM. The roughness decreases slightly as the transformation from the amorphous to the crystalline phase occurs. The chemical compositions of Sb2S3 films were analyzed by EDS, revealing that all films were Sb-rich. The optical parameters were estimated from the transmittance and reflectance spectra recorded by UV-Vis spectroscopy. A reduction in the band gap energy from 2.12 to 1.70 eV with the increase of annealing temperature was also found

Optimized Omnidirectional High-Reflectance Using Octonacci Photonic Crystal for Thermographic Sensing Applications

The transmittance of waves through one-dimensional periodic and Octonacci photonic structures was studied using the theoretical transfer matrix method for both wave-polarization-modes. The first structures were made up of the SiO2 and TiO2 materials. The objective here was to obtain a broad omnidirectional high reflector covering the infrared spectrum of a thermographic camera [1–14 µm] and, especially, to prevent the transmission of emitted human body peak radiation λmax = 9.341 µm. By comparing the periodic and Octonacci structures, we found that the last structure presented a main and wide photonic band gap near this human radiation. For that, we kept only the Octonacci structure for the rest of the study. The first structure did not give the aspired objective; thus, we replaced the TiO2 layers with yttrium barium copper oxide material, and a significant enhancement of the omnidirectional photonic band gap was found for both TE and TM polarization modes. It was shown that the width of this band was sensitive to the Octonacci iteration number and the optical thickness (by changing the reference wavelength), but it was not affected by the ambient temperature. The number of layers and the thickness of the structure was optimized while improving the omnidirectional high reflector properties