Effects of deposition time and temperature on the optical properties of air-annealed chemical bath deposited CdS films

CdS films of over 1-μm thickness were deposited onto glass substrates by chemical bath deposition (CBD). Deposition temperature and time were varied from 40 °C to 60 °C and from 30 min to 4 h, respectively. The highest deposition rate, 6.39 nm/min, was obtained with samples deposited for 90 min at 60 °C. The films deposited at 60 °C for 4 h were found to have the best adhesion and without defects. The optical properties, in particular the optical band gap, depended on film thickness, the deposition and annealing temperatures. Annealing in air resulted in a shift of the absorption edge towards higher wavelengths, i.e., a decrease in the gap value from 2.45 eV to 2.38 eV. The optical band edges of the films were not constant but depended on the annealing temperature. The refractive index, calculated by applying the envelope method on the transmission of the films in wavelengths from 550 nm to 850 nm, was in the range 1.95-2.26. The resistivity determined from dark conductivity measurement, as a function of the annealing temperature, was found to be in the order of 10⁵ Ω cm for samples annealed in air at 250 °C, 3 h, and the activation energy was about 0.22 eV.     

Optical and electrical characterization of CdS thin films

Thin CdS films have been grown by chemical bath (CdCl₂, thiourea, ammonia) deposition (CBD) on SnO₂ (TO)-coated glass substrate for use as window materials in CdS/CdTe solar cells. High-resolution transmission electron microscopy revealed grains with an average size of 10 nm. The structure was predominantly hexagonal with a high density of stacking faults. The film crystallinity improved with annealing in air. Annealing in a CdCl₂ flux increased the grain size considerably and reduced the density of stacking faults. The optical transmission of the as-deposited films indicated a band gap energy of 2.41 eV. Annealing in air reduced the band gap by 0.1 eV. Annealing in CdCl₂ led to a sharper optical absorption edge that remained at 2.41 eV. Similar band gap values were obtained by photocurrent spectroscopy and electroabsorption spectroscopy (EEA) using an electrolyte contact. EEA spectra were broad for the as-deposited and air-annealed samples, but narrower for the CdCl₂-annealed films, reflecting the reduction in stacking fault density. Donor densities of ca. 10¹⁷ cm ^–3 were derived from the film/electrolyte junction capacitance.     

Structural and optical properties of CdS thin films prepared by chemical bath deposition at different ammonia concentration and S/Cd molar ratios

CdS thin films were prepared by chemical bath deposition technique using the precursors of SC(NH₂)₂, CdCl₂, NH₄Cl, NH₃·H₂O and deionized water. The obtained thin films were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive spectrometer, UV–VIS specrophotometry and photoluminescence spectroscopy. The morphology, structural and optical properties of CdS thin films were investigated as a function of ammonia concentration and S/Cd molar ratios in precursors. The results reveal that morphology of CdS films change from flake like into spherical particle like, crystal structure from wurtzite structure to zinc blende structure, S/Cd atom ratios in CdS thin films increase and optical band gap E _g decrease with increasing ammonia concentration in precursors. The room temperature photoluminescence spectrum of CdS thin films shows a strong peak at about 500 nm and a weak peak at about 675 nm.     

Influence of the annealing in nitrogen atmosphere on the XRD, EDX, SEM and electrical properties of chemical bath deposited CdSe thin films

The influence of annealing in nitrogen atmosphere on the structure, optical and electrical properties of cadmium selenide (CdSe) thin films deposited by chemical bath deposition (CBD) onto glass substrates was studied. The samples were annealed in nitrogen atmosphere at various temperatures. A transition from metastable nanocrystalline cubic to stable polycrystalline hexagonal phase has been observed after annealing. The as-deposited CdSe thin films grow in the nanocrystalline cubic phase with optical band gap 1.93 eV. The electrical resistivity of the thin films has been measured in order of 10⁶ Ω cm. The activation energy of the samples has been found to be 0.26–0.19 eV at low temperature region, and 0.36–0.56 eV at high temperature region. It was also found that the activation energy and the resistivity of the films decrease with the increasing annealing temperature.     

Optical and structural properties of chemically deposited CdS thin films on polyethylene naphthalate substrates

CdS thin films were deposited on polyethylene naphthalate substrates by means of the chemical bath deposition technique in an ammonia-free cadmium-sodium citrate system. Three sets of CdS films were grown in precursor solutions with different contents of Cd and thiourea maintaining constant the concentration ratios [Cd]/[thiourea] and [Cd]/[sodium citrate] at 0.2 and 0.1 M/M, respectively. The concentrations of cadmium in the reaction solutions were 0.01, 7.5 × 10⁻³ and 6.8 × 10⁻³ M, respectively. The three sets of CdS films were homogeneous, hard, specularly reflecting, yellowish and adhered very well to the plastic substrates, quite similar to those deposited on glass substrates. The structural and optical properties of the CdS films were determined from X-ray diffraction, optical transmission and reflection spectroscopy and atomic force microscopy measurements. We found that the properties of the films depend on both the amount of Cd in the growth solutions and on the deposition time. The increasing of Cd concentration in the reaction solution yield to thicker CdS films with smaller grain size, shorter lattice constant, and higher energy band gap. The energy band gap of the CdS films varied in the range 2.42-2.54 eV depending on the precursor solution. The properties of the films were analyzed in terms of the growth mechanisms during the chemical deposition of CdS layers.     

Structural, photoluminescence and optical properties of chemically deposited (Cd1−xBix)S thin films as a function of dopant concentration

In this study, (Cd_1?xBi_x)S thin films were successfully deposited on suitably cleaned glass substrate at 60 °C temperature, using the chemical bath deposition technique. After deposition, the films were also annealed at 400 °C for 2 min in air. The structural properties of the deposited films were characterized using X-ray diffraction and AFM. Formation of cubic structure with preferential orientation along the (111) plane was confirmed together with BiS second phase from structural analysis. The interplanar spacing, lattice constant, and crystallite size of (Cd_1?xBi_x)S thin films were calculated by the XRD. The crystallite size of the un-doped CdS thin films was found to be 7.84 nm, which increased to 11.1 nm with increasing Bi content from 0 to 10 %. The surface roughness of the films was measured by AFM studies. The photoluminescence spectra were observed at red shifted band edge peak with increasing doping concentration of Bi from 0 to 5 % in the un-doped CdS thin films. The optical properties of the films are estimated using optical absorption and transmission spectra in the range of 400–800 nm using UV–VIS spectrophotometer. The optical band gap energy of the films was found to be decreased from 2.44 to 2.23 eV with the Bi content being from 0 to 5 %. After annealing, the band gap of these films further decreased.     

One-step chemical bath deposition and photocatalytic activity of Cu2O thin films with orientation and size controlled by a chelating agent

Nanocrystalline cuprous oxide (Cu₂O) thin films were prepared via a one-step chemical bath deposition (CBD) method. The effects of a chelating agent on the orientation, morphology, crystallite size, and photocatalytic activity of the thin films were carefully examined using X-ray diffractometry, scanning electron microscopy, and UV–vis spectrophotometry. The results confirmed that the crystallite size as well as the orientation of the films was dependent on the volume of trisodium citrate (TSC), demonstrating that the band gap ranged from 2.71 eV to 2.49 eV. The morphology and number density of the thin films also depended on the volume of TSC. In addition, the obtained Cu₂O thin films could degrade methyl orange (MO) efficiently in the presence of H₂O₂ under visible-light irradiation, and the mechanism for the enhanced photocatalytic activity of the Cu₂O thin films with the assistance of H₂O₂ was also explored in detail.     

Optical and structural properties of CuSbS2 thin films grown by thermal evaporation method

Structural, optical and electrical properties of CuSbS₂ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuSbS₂ thin films were carried out at substrate temperatures in the temperature range 100-200 °C. The structure and composition were characterized by XRD, SEM and EDX. X-ray diffraction revealed that the films are (111) oriented upon substrate temperature 170 °C and amorphous for the substrate temperatures below 170 °C. No secondary phases are observed for all the films. The optical absorption coefficients and band gaps of the films were estimated by optical transmission and reflection measurements at room temperature. Strong absorption coefficients in the range 10⁵-10⁶ cm^− 1 at 500 nm were found. The direct gaps Eg lie between 0.91-1.89 eV range. It is observed that there is a decrease in optical band gap Eg with increasing the substrate temperature. Resistivity of 0.03-0.96 Ω cm, in dependence on substrate temperature was characterized. The all unheated films exhibit p-type conductivity. The characteristics reported here also offer perspective for CuSbS₂ as an absorber material in solar cells applications.     

Brush electrodeposited CdS films on low temperature substrates

Cadmium sulphide films were deposited by the brush plating technique on titanium and conducting glass substrates using a current density of 80 mA cm^− 2. X-ray diffraction studies indicated the polycrystalline nature of the films with hexagonal structure. As the deposition temperature decreased, the peaks were broad indicating the formation of nanocrystallites. Optical absorption measurements yielded band gap values in the range of 2.39-3.10 eV as the deposition temperature decreases. XPS studies confirmed the formation of CdS. Atomic force microscope studies indicated the roughness of the films decreases with the decrease of deposition temperature. The as deposited films were photoactive.     

Chemical bath deposition and characterization of CdSe thin films for optoelectronic applications

Cadmium selenide (CdSe) thin films of high crystalline quality on glass substrate have been prepared by chemical bath deposition technique from an aqueous bath containing tetramine cadmium and sodium selenosulphate. Structural analysis using XRD shows that the film is single phase, crystallized in hexagonal structure with preferred growth in (111) direction. The energy band gap calculated from the absorption spectra of unannealed CdSe thin films shows an optical band gap of 1.8 eV and absorption coefficient near band edge (α)—0.58 × 10⁵ cm⁻¹. The conductivity of CdSe thin films is n-type.     

Structure and optical properties of InN and InAlN films grown by rf magnetron sputtering

The structure and optical properties of InN and In-rich InAlN films grown by magnetron sputtering were investigated. The XRD results show that these films are highly c-axis oriented. The film morphology and microstructure of these films were observed by AFM and SEM which reveals that the films grown in island growth mode. Optical properties of these films were studied by absorption method. The band gap energy of the InN film grown under substrate temperature of 400 °C is 1.38 eV. By studying the E _g values of InN films deposited under different substrate temperature, the Burstein-Moss effect on band gap of InN was examined. The significant band gap bowing of our In-rich InAlN films was found to be correlated with the In contents. The bowing parameter of 3.68 eV was obtained which is in agreement with previous theoretical predictions.     

Growth of cadmium selenide layers by electrodeposition

Cadmium selenide (CdSe) films have been electrodeposited from a bath containing CdSO₄ and SeO₂. The pH of the bath was around 2. The deposition was done by short circuiting different substrates like Indium Tin Oxide ITO, molybdenum, sodium selenosulphite etc. to an easily oxidizable electrode (such as Al/Cd) in an electrolytic bath. The temperature of the deposition bath was varied in the range 60 to 85 ° C. The as-grown films were characterized by X-ray diffraction and scanning electron microscopy. Electrical characterization of the ITO/ CdSe/In structure was made by studying the current-voltage characteristics. Optical absorption measurements yielded a direct band gap around 1.65eV.     

Phase change and optical band gap behavior of Ge-Te-Ga thin films prepared by thermal evaporation

The amorphous Ge_11.4Te_86.4Ga_2.2 chalcogenide thin films were prepared by thermal evaporation onto chemically cleaned glass substrates. Properties measurements include X-ray diffraction (XRD), Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), Four-point probe and VIS-NIR transmission spectra. The allowed indirect transition optical band gap and activation energy of samples were calculated according to the classical Tauc equation and Kissinger's equation, respectively. The results show that there is an amorphous-to-crystalline phase transition of Ge_11.4Te_86.4Ga_2.2 thin film. The investigated film has high crystallization temperature (∼200 °C) and activation energy (2.48 eV), indicating the film has good amorphous stability. The sheet resistance of the crystalline state is ∼10 Ω/and the amorphous/crystalline resistance ratio is about 10⁵. Besides, a wide optical band gap (0.653 eV) of Ge_11.4Te_86.4Ga_2.2 is obtained, indicating that the material possesses a low threshold current from amorphous-to-crystalline state for phase-change memory application.     

Characterization of nanocrystalline cadmium telluride thin films grown by successive ionic layer adsorption and reaction (SILAR) method

Structural, electrical and optical characteristics of CdTe thin films prepared by a chemical deposition method, successive ionic layer adsorption and reaction (SILAR), are described. For deposition of CdTe thin films, cadmium acetate was used as cationic and sodium tellurite as anionic precursor in aqueous medium. In this process hydrazine hydrate is used as reducing agent and NH₄OH as the catalytic for the decomposition of hydrazine. By conducting several trials optimization of the adsorption, reaction and rinsing time duration for CdTe thin film deposition was done. In this paper the structural, optical and electrical properties of CdTe film are reported. The XRD pattern shows that films are nanocrystalline in nature. The resistivity is found to be of the order of 411 × 10³ Ω-cm at 523 K temperature with an activation energy of ∼ 0.2 eV. The optical absorption studies show that films have direct band gap (1.41 eV).     

Formation and properties of cadmium sulfide buffer layer for CIGS solar cells grown using hot plate bath deposition

In the present study, cadmium sulfide (CdS) thin films were deposited on different substrates [soda glass, fluoride doped tin oxide, and tin doped indium oxide (ITO) coated glass] by a hot plate method. To control the thickness and the reproducibility of the sample production, the thin films were coated at different temperatures and deposition times. The CdS thin films were heated at 400 °C in air and forming gas (FG) atmosphere to investigate the effect of the annealing temperatures. The thickness of the samples, measured by ellipsometry, could be controlled by the deposition time and temperature of the hot plate. The phase formation and structural properties of CdS thin films were studied by X-ray diffraction and scanning electron microscopy, whereas the optical properties were obtained by UV–vis spectroscopy. A hexagonal crystal structure was observed for CdS thin films and the crystallinity improved upon annealing. The structural and optical properties of CdS thin films were also enhanced by annealing at 400 °C in FG atmosphere (95 % N₂, 5 % H₂). The optical band gap was changed from 2.25 to 2.40 eV at different annealing temperatures and gas atmospheres. A higher electrical conductivity, for the sample annealed at FG, was noticed. The samples deposited on ITO and annealed in FG atmosphere showed the best structural and electrical properties compared to the other samples. CdS thin films can be widely used for application as a buffer layer for copper–indium–gallium–selenide solar cells.     

Synthesis and properties of epitaxial SnO2 films deposited on MgO (100) by MOCVD

Epitaxial tin oxide (SnO₂) thin films have been prepared on MgO (100) substrates at 500-600 °C by metalorganic chemical vapor deposition method. Structural and optical properties of the films have been investigated in detail. The obtained films were pure SnO₂ with the tetragonal rutile structure. An in-plane orientation relationship of SnO₂ (110) [010]//MgO (200) [110] between the film and substrate was determined. Two variant structure of SnO₂ were analyzed. The structure of the film deposited at 600 °C was investigated by high-resolution transmission electron microscopy, and an epitaxial structure was observed. The absolute average transmittance of the SnO₂ film at 600 °C in the visible range exceeded 90%. The optical band gap of the film was about 3.93 eV.     

Properties of BGO thin films under the influence of gamma radiation

It is important to know the behaviour of materials under the influence of radiation for the effective design of novel sensor systems. Optical properties of bismuth germinate (Bi₄Ge₃O₁₂—BGO) thin films were investigated in terms of their perception to gamma radiation exposure. An Edwards E306A vacuum thermal coating system was used for thin films deposition. BGO films with a thickness of 200 nm were exposed to a disk-type ¹³⁷Cs gamma radiation source with an activity of 370 kBq. Optical properties of the films were investigated using CARY IE UV-Visible Spectrophotometer. Calculated optical band gap for as-deposited BGO thin film was 1.95 eV. Gamma radiation induced changes in the optical properties of thin films, which could be explained by the variation in the degree of disorder. From the density-of-state model, it is known that optical band gap decreases with an increasing degree of disorder of the amorphous phase.Electrical properties of BGO thin films were recorded in real time using a low power capacitive interface system with a high resolution, which is based on Delta-sigma modulator. At doses from 0 to 1.5 mGy little if any changes in the capacitance were measured. This could be explained by co-existence of two processes, namely creation and annihilation of defects under the influence of radiation. After a threshold dose of 1.5 mGy creation of defects becomes more prevailing and the BGO film capacitance has gradually increased in value from 2.97 pF to 7.09 pF after irradiation with a 2.44 mGy dose.     

Property variations of direct-current reactive magnetron sputtered copper oxide thin films deposited at different oxygen partial pressures

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were deposited on glass substrates at different oxygen partial pressures by direct-current reactive magnetron sputtering of pure copper target in a mixture of argon and oxygen gases. Oxygen partial pressure was found to be a crucial parameter in controlling the phases and, thus, the physical properties of the deposited copper oxide thin films. Single-phase Cu₂O thin films with cubic structure were obtained at low oxygen partial pressure between 0.147 Pa and 0.200 Pa while higher oxygen partial pressure promoted the formation of CuO thin films with base-centered monoclinic structure. Polycrystalline Cu₂O thin films deposited with oxygen partial pressure at 0.147 Pa possessed the lowest p-type resistivity of 1.76 Ω cm as well as an optical band gap of 2.01 eV. On the other hand, polycrystalline CuO thin films deposited with oxygen partial pressure at 0.320 Pa were also single phase but showed a n-type resistivity of 0.19 Ω cm along with an optical band gap of 1.58 eV.     

Structural,optical and microscopic properties of chemically deposited Mo<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>Se<Subscript>2</Subscript> thin films

Mo_0.5W_0.5Se₂ thin films were obtained by using relative simple chemical route at room temperature. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, scanning electron microscope, optical and electrical properties. The grown films were found to be uniform, well adherent to substrate and brown in color. The X-ray diffraction pattern shows that thin films have a hexagonal phase. Optical properties show a direct band gap nature with band gap energy 1.44 eV and having specific electrical conductivity in the order of 10⁻⁵ (Ωcm)⁻¹.     

Chemical bath deposition of CdS thin films doped with Zn and Cu

Zn- and Cu-doped CdS thin films were deposited onto glass substrates by the chemical bath technique. ZnCl₂ and CuCl₂ were incorporated as dopant agents into the conventional CdS chemical bath in order to promote the CdS doping process. The effect of the deposition time and the doping concentration on the physical properties of CdS films were investigated. The morphology, thickness, bandgap energy, crystalline structure and elemental composition of Zn- and Cu-doped CdS films were investigated and compared to the undoped CdS films properties. Both Zn- and Cu-doped CdS films presented a cubic crystalline structure with (1 1 1) as the preferential orientation. Lower values of the bandgap energy were observed for the doped CdS films as compared to those of the undoped CdS films. Zn-doped CdS films presented higher thickness and roughness values than those of Cu-doped CdS films. From the photoluminescence results, it is suggested that the inclusion of Zn and Cu into CdS crystalline structure promotes the formation of acceptor levels above CdS valence band, resulting in lower bandgap energy values for the doped CdS films.