Optical and electrical measurement of FeSe2 thin films obtained at low temperature

FeSe₂ thin films were prepared at low temperature by thermal annealing at 350 °C during 6 h of sequentially evaporated iron and selenium films under selenium atmosphere. The structural, optical and electrical characteristics were investigated. The roughness of films (~76 nm) was confirmed by AFM images. Moreover, optical band gap of FeSe₂, which was evaluated as nearly 1.11 eV and confirmed by the electrical study which yielded a value in the order of 1.08 eV. The electrical conductivity, conduction mechanism, dielectric properties and relaxation model of theses thin films were studied using impedance spectroscopy technique in the frequency range 5 Hz–13 MHz under various temperatures (180–300 °C). Besides, complex impedance and AC conductivity have been investigated on the basis of frequency and temperature dependence.     

Effect of substrate temperature on structural,morphological, optical and electrical properties of MnIn2S4 thin films prepared by nebulizer spray pyrolysis technique

Manganese indium sulphide (MnIn₂S₄) thin films were deposited using an aqueous solution of MnCl₂, InCl₃ and (NH₂)₂CS in the molar ratio 1:2:4 by simple chemical spray pyrolysis technique. The thin film substrates were annealed in the temperature range between 250 and 350 °C to study their various physical properties. The structural properties as studied by X-ray diffraction showed that MnIn₂S₄ thin films have cubic spinel structure. The formation of cube and needle shaped grains was clearly observed from FE-SEM analysis. The energy dispersive spectrum (EDS) predicts the presence of Mn, In and S in the synthesized thin film. From the optical studies, it is analyzed that the maximum absorption co-efficient is in the order between 10⁴ and 10⁵ cm⁻¹ and the maximum transmittance (75%) was noted in the visible and infrared regions. It is noted that, the band gap energy decreases (from 3.20 to 2.77 eV) with an increase of substrate temperature (from 250 to 350 °C). The observations from photoluminescence studies confirm the emission of blue, green, yellow and red bands which corresponds to the wavelength range 370–680 nm. Moreover, from the electrical studies, it is observed that, as the substrate temperature increases the conductivity also increases in the range 0.29–0.41×10⁻⁴ Ω⁻¹ m⁻¹. This confirms the highly semiconducting nature of the film. The thickness of the films was also measured and the values ranged between 537 nm (250 °C) to 483 nm (350 °C). This indicates that, as the substrate temperature increases, the thickness of the film decreases. From the present study, it is reported that the MnIn₂S₄ thin films are polycrystalline in nature and can be used as a suitable ternary semiconductor material for photovoltaic applications.     

Low-cost TiO2/Sb2(S,Se)3 heterojunction thin film solar cell fabricated by sol-gel and chemical bath deposition

Low cost TiO₂/ Sb₂(S, Se)₃ heterojunction thin film solar cell are prepared successfully by using sol-gel and chemical bath deposition. At first, TiO₂ thin film is prepared on the ITO-coated glass substrate by a simple sol-gel and dip-coating method. Subsequently, Sb₂(S, Se)₃ film is fabricated on TiO₂ by selenizing the Sb₂S₃ film prepared by chemical bath deposition (CBD). The heat-treated process of TiO₂ and Sb₂(S, Se)₃ films has been discussed, respectively. After being heat-treated at 550 °C for TiO₂ and 290 °C for Sb₂(S, Se)₃ films, the photovoltaic devices are completed with the conductive graphite as electrode. The J-V characteristics of TiO₂/ Sb₂(S, Se)₃ solar cell are measured and the open circuit voltage (V_oc) of this cell is about 350 mV.     

Influence of annealing temperature on the phase composition and optical properties of CuInS2 films

We studied the growth of CuInS₂ thin films by single-source evaporation of CuInS₂ powder in a high-vacuum system with a base pressure of 10^?3 Pa. After evaporation, the films were annealed in a sulfur atmosphere at temperatures from 200 to 500 °C for 1 h. XRD curves and Raman spectra of the films demonstrated that chalcopyrite CuInS₂ was the major crystalline phase. The morphology of Cu_xS exhibited a star-like structure, which we report for the first time. The phase composition and optical properties of our polycrystalline thin films were effectively modified by annealing in S. For films annealed at 200 and 350 °C, a secondary CuIn₁₁S₁₇ phase appeared, which may be related to solid-state reaction in the S atmosphere. This secondary CuIn₁₁S₁₇ phase has not been widely reported in previous studies. After annealing at 500 °C, only a chalcopyrite phase was detected, with bandgap energy of 1.46 eV, which is nearly identical to the optimal bandgap energy (1.5 eV) of single-crystal CuInS₂. This indicates that the composition of the CuInS₂ film annealed at 500 °C was nearly stoichiometric. The bandgap of the samples first increased and then decreased with increasing annealing temperature, which may be attributed to an increase in grain size, the secondary CuIn₁₁S₁₇ phase, and deviation from stoichiometry.     

Antimony sulfide (Sb2S3) thin films by pulse electrodeposition: Effect of thermal treatment on structural,optical and electrical properties

Antimony sulfide films have been deposited by pulse electrodeposition on Fluorine doped SnO₂ coated glass substrates from aqueous solutions containing SbCl₃ and Na₂S₂O₃. The crystalline structure of the films was characterized by X-ray diffraction, Raman spectroscopy and TEM analysis. The deposited films were amorphous and upon annealing in nitrogen/sulfur atmosphere at 250 °C for 30 min, the films started to become crystalline with X-ray diffraction pattern matching that of stibnite, Sb₂S₃, (JCPDS 6-0474). AFM images revealed that Sb₂S₃ films have uniformly distributed grains on the surface and the grain agglomeration occurs with annealing. The optical band gap calculated from the transmittance and the reflectance studies were 2.2 and 1.65 eV for as deposited and 300 °C annealed films, respectively. The annealed films were photosensitive and exhibited photo-to-dark current ratio of two orders of magnitude at 1 kW/m² tungsten halogen radiation.     

Properties of In2O3 films obtained by thermal oxidation of sprayed In2S3

In₂S₃ thin films were grown by the chemical spray pyrolysis (CSP) method using indium chloride and thiourea as precursors at a molar ratio of S:In=2.5. The deposition was carried out at 350 °C on quartz substrates. The film thickness is about 1 µm. The films were then annealed for 2 h at 550, 600, 650 and 700 °C in oxygen flow. This process allows the transformation of nanocrystal In₂O₃ from In₂S₃ and the reaction is complete at 600 °C. X-ray diffraction spectra show that In₂O₃ films are polycrystalline with a cubic phase and preferentially oriented towards (222). The film grain size increases from 19 to 25 nm and RMS values increase from 9 to 30 nm. In₂O₃ films exhibit transparency over 70–85% in the visible and infrared regions due to the thickness and crystalline properties of the films. The optical band gap is found to vary in the range 3.87–3.95 eV for direct transitions. Hall effect measurements at room temperature show that resistivity is decreased from 117 to 27 Ω cm. A carrier concentration of 1×10¹⁶ cm^?3 and mobility of about 117 cm² V^?1 s^?1 are obtained at 700 °C.     

Resistive switching behavior of Sb2S3 thin film prepared by chemical bath deposition

The chalcogenides are the excellent memristor materials. Here we report the resistive switching properties of an amorphous Sb₂S₃ thin film. Sb₂S₃ films were deposited on FTO glass using a low-temperature (10 °C) chemical bath deposition technique. SEM and XRD results indicate that the as-grown Sb₂S₃ film is dense and amorphous with uniform thickness and smooth surface. The Ag/Sb₂S₃/FTO memristor shows typical bipolar switching behavior with low operating voltage, high resistance ratio, long retention time, and good endurance. The electrical tests demonstrate that the switching behavior of the amorphous Sb₂S₃ film is based on electrochemical metallization mechanisms.     

Physical investigations on Sb2S3 sprayed thin film for optoelectronic applications

Sb₂S₃ thin films have been obtained at 250 °C on glass substrates using the spray pyrolysis techniques. The structural study by means of XRD analysis shows that Sb₂S₃ thin film crystallized in the orthorhombic phase. The discussion of some structural constants has been made by means of both XRD and AFM investigations. Moreover, the optical analysis via the transmittance and the reflectance measurements reveals that Sb₂S₃ sprayed thin film has a direct transition with the band gap energy E_g equal to 1.72 eV. The analysis in 300–2500 nm domain of the refractive index data through Wemple–DiDomenico model leads to the single oscillator energy (E₀=2.32 eV), and the dispersion energy (E_d=10.03 eV). The electrical study leads to the dc activation energy is of the order of 0.72 eV and the maximum barrier high is W_M=0.87 eV. From the power exponent variation in terms of the heated temperature, it is found that the mechanism of conduction matches well the correlated barrier hopping CBH model.     

Temperature effect on the physical properties of CuIn11S17 thin films for photovoltaic applications

CuIn₁₁S₁₇ compound was synthesized by horizontal Bridgman method using high-purity copper, indium and sulfur elements. CuIn₁₁S₁₇ thin films were prepared by high vacuum evaporation on glass substrates. The glass substrates were heated at 30, 100 and 200 °C. The structural properties of the powder and the films were investigated using X-ray diffraction (XRD). XRD analysis of thin films revealed that the sample deposited at a room temperature was amorphous in nature while those deposited on heated substrates were polycrystalline with a preferred orientation along the (311) plane of the spinel phase. Ultraviolet–visible (UV–vis) spectroscopy was used to study the optical properties of thin films. The results showed that CuIn₁₁S₁₇ thin films have high absorption coefficient α in the visible range (10⁵–10⁶ cm⁻¹). The band gap E_g of the films decrease from 2.30 to 1.98 eV with increasing the substrate temperature (T_s) from 30 to 200 °C. We exploited the models of Swanepoel, Wemple–DiDomenico and Spitzer–Fan for the analysis of the dispersion of the refractive index n and the determination of the optical constants of the films. Hot probe method showed that CuIn₁₁S₁₇ films deposited at T_s=30 °C and T_s=100 °C are p-type conductivity whereas the sample deposited at T_s=200 °C is highly compensated.     

The effects of carrier gas and substrate temperature on ZnO films prepared by ultrasonic spray pyrolysis

ZnO films were deposited on glass substrates in the temperature range of 350–470 °C under an atmosphere of compressed air or nitrogen (N₂) by using ultrasonic spray pyrolysis technique. Structural, electrical and optical properties of the ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical two-probe and optical transmittance measurements. The ZnO films deposited in the range of 350–430 °C were polycrystalline with the wurtzite hexagonal structure having preferred orientation depending on the substrate temperature. The ZnO films deposited below 400 °C had a preferred (100) orientation while those deposited above 400 °C mostly had a preferred (002) orientation. The resistivity values of ZnO films depended on the types of carrier gas. The ZnO thin films deposited under N₂ atmosphere in the range of 370–410 °C showed dense surface morphologies and resistivity values of 0.6–1.1 Ω-cm, a few orders of magnitude lower than those deposited under compressed air. Hydrogen substition in ZnO possibly contributed to decreasing resistivity in ZnO thin films deposited under N₂ gas. The Hall measurements showed that the behavior of ZnO films deposited at 410 °C under the N₂ atmosphere was n-type with a carrier density of 8.9–9.2×10¹⁶ cm^-3 and mobility of ～70 cm²/Vs. ZnO thin films showed transmission values at 550 nm wavelength in a range of 70–80%. The values of band gaps extrapolated from the transmission results showed bandgap shrinkage in an order of milli electron volts in ZnO films deposited under N₂ compared to those deposited under compressed air. The calculation showed that the bandgap reduction was possibly a result of carrier–carrier interactions.     

Effect of annealing on structural,optical and electrical properties of pulse electrodeposited tin sulfide films

Polycrystalline tin sulfide (SnS) thin films were grown on conducting glass substrates by pulse electrodeposition. The effect of annealing on the physical properties such as structure, morphology, optical, and opto-electronic properties were evaluated to understand the effect of post-deposition treatment for SnS films. Annealing at temperatures higher than 250 °°C resulted in the formation of SnS₂ as a second phase, however, no significant grain growth or morphological changes were observed for films after annealing at 350 °C. A small change in band gap of 0.1 eV observed for films annealed at 350 °C was interpreted as due to the formation of SnS₂ rather than due to morphological changes. This interpretation was supported by X-ray diffractometry, scanning electron microscopy, and Raman spectral data. The electric conduction in the films is controlled by three shallow trap levels with activation energies 0.1, 0.05, and 0.03 eV. The trap with energy 0.03 eV disappeared after annealing at higher temperature, however, the other two traps were unaffected by annealing.     

Effect of thermal annealing on physical properties of vacuum evaporated In2S3 buffer layer for eco-friendly photovoltaic applications

The present communication reports the effect of thermal annealing on the physical properties of In₂S₃ thin films for eco-friendly buffer layer photovoltaic applications. The thin films of thickness 150 nm were deposited on glass and indium tin oxide (ITO) coated glass substrates employing thermal vacuum evaporation technique followed by post-deposition thermal annealing in air atmosphere within a low temperature range 150–450 °C. These as-deposited and annealed films were subjected to the X-ray diffraction (XRD), UV–vis spectrophotometer, current–voltage tests and scanning electron microscopy (SEM) for structural, optical, electrical and surface morphological analysis respectively. The compositional analysis of as-deposited film is also carried out using energy dispersive spectroscopy (EDS). The XRD patterns reveal that the as-deposited and annealed films (≤300 °C) have amorphous nature while films annealed at 450 °C show tetragonal phase of β-In₂S₃ with preferred orientation (109) and polycrystalline in nature. The crystallographic parameters like lattice constant, inter-planner spacing, grain size, internal strain, dislocation density and number of crystallites per unit area are calculated for thermally annealed (450 °C) thin films. The optical band gap was found in the range 2.84–3.04 eV and observed to increase with annealing temperature. The current–voltage characteristics show that the as-deposited and annealed films exhibit linear ohmic behavior. The SEM studies show that the as-deposited and annealed films are uniform, homogeneous and free from crystal defects and voids. The grains in the thin films are similar in size and densely packed and observed to increase with thermal annealing. The experimental results reveal that the thermal annealing play significant role in the structural, optical, electrical and morphological properties of deposited In₂S₃ thin films and may be used as cadmium-free eco-friendly buffer layer for thin films solar cells applications.     

Evaporated iron disulfide thin films with sulfurated annealing treatments

FeS₂ thin films were grown on a glass substrate using a physical vapor deposition technique at room temperature. Subsequently, the thin films were annealed in two different atmospheres: vacuum and vacuum-sulfur. In the vacuum-sulfur atmosphere a graphite box was used as sulfur container and the films were sulfurated successfully at 200–350 ºC. It was found that annealing in a vacuum-sulfur atmosphere was indispensable in order to obtain polycrystalline FeS₂ thin films. The polycrystalline nature and pure phase were determined by XRD and Raman techniques and the electrical properties by the Hall effect. Using the sulfurating technique, the n-type semiconductor was prepared at 200–350 °C and a p-type at 500 °C. The carrier concentrations were between 1.19×10²⁰ and 2.1×10²⁰ cm⁻³. The mobility was 9.96–5.25 cm² V⁻¹ s⁻¹ and the resistivity was 6.31×10⁻² to 1.089×10⁻² Ω cm. The results obtained from EDS showed that the films prepared in the vacuum-sulfur atmosphere were close to stoichiometric and that the indirect band gap varied between 1.03 and 0.945 eV.     

Raman spectroscopic study of In2S3 films prepared by spray pyrolysis

Indium sulfide (In₂S₃) thin films are of interest as buffer layers in chalcopyrite absorber based solar cells; and as media providing two-photon absorption for intermediate-band solar cells. We investigated the suitability of chemical spray pyrolysis (CSP) for growing In₂S₃ thin films in a structural order where indium atoms are preferentially in the octahedral sites. We sprayed aqueous or alcoholic solutions of indium chloride (InCl₃) and thiourea (SC(NH₂)₂) precursors onto a substrate with surface temperatures (T_S) of 205, 230, 275 and 320 °C. The as-deposited films grown from aqueous solutions were annealed in 5% H₂S containing atmosphere at 500 °C. We used Raman spectroscopy, X-ray diffraction and Energy Dispersive X-ray spectroscopy to evaluate the effect of growth temperature and the effect of annealing on the film structure and stoichiometry. The use of alcoholic solvent instead of aqueous allows us to use much lower T_S while preserving the quality of the β-In₂S₃ films obtained. Similarly, films with increased stoichiometry and quality are present at a higher T_S; and when annealed. The annealing of the films grown at T_S of 205 °C results in a much higher gain of the crystal quality compared to the gain when annealing the films grown at T_S of 320 °C, although the quality remain higher when deposited at T_S of 320 °C. Simultaneously with the increase of the film quality, there is a sign of increased quality of the crystal ordering with indium in the octahedral sites. Such a crystal ordering favor the use of CSP deposited In₂S₃ films in the intermediate band solar cells.     

Optical and ac conductivity investigations on Sn doped Ag2S thin films under the structural transition framework

This work deals with further optical and electrical investigations on Sn content in Ag₂S sprayed thin films and the beneficial effect of using this type of doping in addition to the results recently reported by R. Boughalmi, A. Boukhachem, I. Gaeid, K. Boubaker, M. Bouhafs, M. Amlouk, Mater. Sci. Semicond. Process. 16 (2013) 1584. The refractive index and extinction coefficient values in terms of Sn content were deduced from transmittance and reflectance data. Moreover, study of dielectric constants has been conducted; the dispersion parameters and high- frequency dielectric constant are determined. Finally, the electrical conductivity and conduction mechanism of these films are studied using an impedance spectroscopy technique in the frequency range 5 Hz–13 MHz at various temperatures (100–230 °C). Besides, the temperature dependence of ac conductivity measurements has been analyzed under the structural transition framework from β- to α-Ag₂S phases.     

Electrical measurements of dielectric properties of molybdenum-doped zinc oxide thin films

Effects of molybdenum element content on electrical conductivity of ZnO sprayed thin films were investigated using the impedance spectroscopy method in the frequency ranging from 5 Hz to 13 MHz for temperature lying in 300–475 °C domain. It is observed that AC conductivity is a power law. The values of dielectric constants ε₁ and ε₂ were found to decrease with frequency and increase with temperature. The activation energy determined from the plot of both DC conductivity and the hopping frequency with 1000/T shows that the hopping conduction is the dominant mechanism. Also, experimental data of DC conductivity were analyzed using the small polaron hopping model. The impedance analysis of undoped ZnO and Mo-doped ZnO (1% and 2%) shows only one semicircle implying the response originated from a single capacitive element corresponding to the bulk grains. However, the same analysis for ZnO:Mo (3% ) shows two semicircles which proves the existence of grain boundaries. Finally, analyses of polaron hopping mechanism and Urbach tailing allow some explanations of these transport phenomena. This study shows an effective variation of electrical measurements of Mo-doped ZnO films in terms of temperature leading to possible use of such films as gas sensors.     

Structural,chemical, and electrical properties of Y2O3 thin films grown by atomic layer deposition with an (iPrCp)2Y(iPr-amd) precursor

Y₂O₃ thin films were grown by atomic layer deposition (ALD) through a heteroleptic liquid (iPrCp)₂Y(iPr-amd) precursor at 350 °C. The structural and chemical properties of both as-deposited and annealed Y₂O₃ films at 500 °C and 700 °C are analyzed by atomic force microscopy for variation in surface roughness, X-ray diffraction for crystalline structure, and X-ray photoelectron spectroscopy for chemical states. The as-deposited Y₂O₃ film shows the same crystalline orientation along the plane (222), a stoichiometric state, and minimal hydroxylate formation up to 700 °C. Being the dielectric layer in the metal-oxide-semiconductor capacitor, the as-deposited ALD-Y₂O₃ films with liquid (iPrCp)₂Y(iPr-amd) precursor without any post-deposition annealing show the much lower leakage density than ALD-Y₂O₃ with solid Y(MeCp)₃.     

Effect of zinc doping and temperature on the properties of sprayed CuInS2 thin films

Copper indium disulfide (CuInS₂) is an efficient absorber material for photovoltaic and solar cell applications. The structural, optical, photoluminescence properties and electrical conductivities could be controlled and modified by suitably doping CuInS₂ thin films with dopants such as Zn, Sn, Bi, Cd, Na, N, O, P and As. In this work Zn (0.01 M) doped CuInS₂ thin films are (Cu/In=1.25) deposited on to glass substrates in the temperature range 300–400 °C. It is observed that the film growth temperature, ion ratio (Cu/In=1.25) and Zn-doping affect structural, optical, photoluminescence and electrical properties of sprayed CuInS₂ thin films. As the XRD patterns depict, Zn-doping facilitates the growth of CuInS₂ thin films along (112) preferred plane and in other characteristic planes. The EDAX results confirm the presence of Cu, In, S and Zn in the films. The optical studies show, about 90% of light transmission occurs in the IR regions; hence Zn-doped CuInS₂ can be used as an IR transmitter. The absorption coefficient (α) in the UV–visible region is found to be in the order of 10⁴–10⁵ cm⁻¹ which is the optimum value for an efficient absorber. The optical band gap energies increase with increase of temperatures (1.66–1.78 eV). SEM photographs reveal crystalline and amorphous nature of the films at various temperature ranges. Photoluminescence study shows that well defined broad Blue and Green band emissions are exhibited by Zn-doped CuInS₂ thin films. All the films present low resistivity (ρ) values and exhibit semiconducting nature. An evolution of p-type to n-type conductivity is obtained in the temperature range 325–350 °C. Hence, Zn species can be used as a donor and acceptor impurity in CuInS₂ thin films to fabricate efficient solar cells, photovoltaic devices and good IR Transmitters.     

Physical investigations on (In2S3)x(In2O3)y and In2S3−xSex thin films processed through In2S3 annealing in air and selenide atmosphere

In₂S_3−xSe_x and (In₂S₃)_x(In₂O₃)_y thin films have been prepared on glass substrates using appropriate heat treatments of In evaporated thin films. X-ray analysis shows that In thin films which were annealed under sulfur atmosphere at 350 °C were mainly formed by In₂S₃. A heat treatment of this binary in air at 400 °C during one hour leads to (In₂S₃)_x(In₂O₃)_y ternary material which has a tetragonal structure with a preferred orientation of the crystallites along the (109) direction. Similarly, a heat treatment of In₂S₃ in selenium atmosphere at 350 °C during six hours leads to a new In₂S_3−xSe_x ternary material having tetragonal body centered structure with a preferred orientation of the crystallites along the (109) direction. Optical band gap, refractive index and extinction coefficient values of In₂S_3−xSe_x and (In₂S₃)_x(In₂O₃)_y thin films have been reached. Moreover, correlations between optical conductivity, XRD, AFM and Urbach energy of such ternary thin films have been discussed. Finally, the recorded formation disparity between the quaternary (In₂S₃)_x(In₂O₃)_y and ternary In₂S_3−xSe_x compounds has been discussed in terms of the Simha–Somcynsky and Lattice Compatibility theories.     

Substrate temperature effect on structural,optical and electrical properties of vacuum evaporated SnO2 thin films

Tin oxide (SnO₂) thin films were deposited on glass substrates by thermal evaporation at different substrate temperatures. Increasing substrate temperature (T_s) from 250 to 450 °C reduced resistivity of SnO₂ thin films from 18×10⁻⁴ to 4×10⁻⁴▒ Ω ▒cm. Further increase of temperature up to 550 °C had no effect on the resistivity. For films prepared at 450 °C, high transparency (91.5%) over the visible wavelength region of spectrum was obtained. Refractive index and porosity of the layers were also calculated. A direct band gap at different substrate temperatures is in the range of 3.55−3.77 eV. X-ray diffraction (XRD) results suggested that all films were amorphous in structure at lower substrate temperatures, while crystalline SnO₂ films were obtained at higher temperatures. Scanning electron microscopy images showed that the grain size and crystallinity of films depend on the substrate temperature. SnO₂ films prepared at 550 °C have a very smooth surface with an RMS roughness of 0.38 nm.