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.     

Characterization of In<Subscript>1 − x</Subscript>Cd<Subscript>x</Subscript>S,In<Subscript>2</Subscript>S<Subscript>3</Subscript> and CdS thin films grown by SILAR method

Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit In_1???xCd_xS, In₂S₃ and CdS thin films on glass substrate at room temperature. The crystal structure and crystal size of the thin films were characterized by X-ray diffraction (XRD) method. Scanning Electron Microscopy (SEM) was used to determine morphology and composition of the films. Optical and electrical properties of these films have been investigated as a function of temperature. The photoluminescence measurements were carried out at room temperature and absorption measurements were carried out in the temperature range 10–320 K with a step of 10 K. The band gap energies for CdS, In_0.8Cd_0.2S, In_0.6Cd_0.4S, In_0.4Cd_0.6S, In_0.2Cd_0.8S and In₂S₃ thin films were found as 2.22 eV, 2.56 eV, 2.52 eV, 2.46 eV, 2.38 eV, and 2.72 eV, respectively. The refractive indices (n), optical static and high frequency dielectric constants (\({\in }_{0}\), \({\in }_{{\infty}}\)) values have been calculated by using the energy bandgap values. The electrical resistivity of CdS, Cd_0.5In_0.5S and In₂S₃ thin films have been determined using a ‘dc’ two probe method, in the temperature range of 300–450 K. The electrical resistivity values have been calculated at 300 K.     

Effect of deposition time on structural, optical and photoluminescence properties of Cd0.9Zn0.1S thin films by chemical bath deposition method

The present work investigates the effect of deposition times on the structural, optical and photoluminescence properties of Cd_0.9Zn_0.1S thin films deposited on glass substrate by chemical bath deposition method. The deposition time was varied from 30 to 90 min. The deposited films were uniform and adherent to the glass substrates and amorphous in nature. Structural, optical and photoluminescence properties of Cd_0.9Zn_0.1S thin films were studied through X-ray diffraction, energy dispersive X-ray, scanning electron microscopy, UV–Vis absorption, fourier transform infra red spectroscopy and photoluminescence spectroscopy. The average crystal size was increased from ~1.3 to 2.5 nm with increase in deposition times. The absorption of the films was increased and the absorption peak shifted to lower wavelength side when deposition time increases. The increased energy gap from 2.4 to 2.49 eV with deposition time was due to quantum size effect and better crystallization. The presence of functional groups and chemical bonding were confirmed by FTIR. PL spectra showed two well distinct and strong bands; blue band around 407–415 nm and green band around 537–541 nm due to size effect.     

Synthesis of Cu<Subscript>2</Subscript>ZnSn(S<Subscript>x</Subscript>Se<Subscript>1−x</Subscript>)<Subscript>4</Subscript> thin films directly on transparent conductive glass substrates by solvothermal method

In this paper, the single-step solvothermal method was proposed to grow directly Cu₂ZnSn (S_xSe_1?x)₄ (CZTSSe) thin films on FTO substrates. The composition ‘x’ was varied by changing the molar ratios of thiourea to selenourea in the precursor solutions. The effects of the molar ratios of thiourea to selenourea on the structure, morphology and optical properties of CZTSSe thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, energy dispersive spectrometry and UV–Vis spectrophotometry. The results indicated that CZTSSe thin films are composed of a large number of uniform sphere-like particles, and the diameter of particles varies from 600 to 280 nm when the molar ratios is changed from 1 to 0. The major XRD diffraction peaks shift towards lower diffraction angles, the Raman peak position of A1 mode of CZTSSe thin films moves consecutively towards the lower frequency due to the S replacement by Se. CZTS and CZTSe thin films are single kesterite structure, however, CZTSSe thin films are mixture structure of kesterite and wurtzite. By varying the molar ratios of thiourea to selenourea in the precursor solution, the atom ratios of S/Se in CZTSSe NCs thin films can be well controlled over the whole range, resulting in tunable optical band gap from 1.54 to 1.38 eV.     

Characterization of CBD–CdS nanocrystals doped with Co<Superscript>2+</Superscript>

Co-doped CdS nanofilms are synthesised by chemical bath deposition growth technique at the temperature of 60?±?2 °C. The cobalt molar fraction was ranged from 0 ≤ x ≤ 5.47, which was determined by energy-dispersive X-ray spectroscopy. The X-ray diffraction shows that the nanofilms are of CoS–CdS nanocomposites with individual CdS and CoS crystalline planes. The Co-doped CdS crystalline phase was zinc-blende that was determined by X-ray diffraction and confirmed by Raman spectroscopy. The average grain size of the CdS films was ranged from 2.56 to 1.67 nm that was determined by Debye–Scherrer equation from ZB (111) direction and it was confirmed by Wang equation and high resolution transmission electron microscopy (HRTEM). Raman scattering shows that the CdS lattice dynamics is characteristic of a bimodal behaviour, in which the first optical longitudinal mode denotes the characteristic peak at 305 cm^?1 of the CdS nanocrystals that is associated with the cobalt incorporation. Nanofilms present two main bandgaps at ~?2.56 and 3.80 eV, which are attributed to single CdS and quantum-confinement due to nanocrystals size. The increase in band gap with increase in cobalt concentration suggests intermetallic compound of CoS (E_g = 1.60 eV) with CdS (E_g = 2.44 eV). The CdS nanocrystals size was ranged from 2.46 to 1.81 nm that was determined from ZB (111) direction by Debye–Scherrer equation and confirmed by the Wang equation. The room-temperature photoluminescence of the Co-doped CdS presents well-resolved radiative bands associated to structural defects and with the quantum-confinement. For the Co-doped CdS the photoluminescence intensity increases indicate a high-passivation of the nanocrystals.     

Sulfurization time effects on the growth of Cu2ZnSnS4 thin films by solution method

Cu₂ZnSnS₄ (CZTS) films were obtained by sulfurizing (Cu, Sn) S/ZnS structured precursors prepared by a combination of the successive ionic layer absorption and reaction method and the chemical bath deposition method, respectively. The effect of sulfurization time on structure, composition and optical properties of these CZTS thin films was studied. The results of energy dispersive spectroscopy indicate that the annealed CZTS thin films are of Cu-poor and Zn-rich states. The X-ray diffraction studies reveal that Cu_2?x S phase exists in the annealed CZTS thin film prepared by sulfurization for 20 min, while the Raman spectroscopy analysis shows that there is a small Cu₂SnS₃ phase existing in those by sulfurization for 20 and 40 min. The band gap (E _g ) of the annealed CZTS thin films, which are determined by reflection spectroscopy, varies from 1.49 to 1.56 eV depending on sulfurization time. The best CZTS thin film is the one prepared by sulfurization for 80 min, exhibiting a single kesterite structure, dense morphology, ideal band gap (E _g  = 1.55 eV) and high optical absorption coefficient (>10⁴ cm^?1).     

Structural,optical and photoluminescence properties of hybrid metal–organic halide perovskite thin films prepared by a single step solution method

We report an inexpensive single step solution method to produce hybrid organic–inorganic lead iodide perovskite thin films for their application to photovoltaic devices. Using PbI₂ and CH₃NH₃Cl (MACl) as precursors for this single step solution method, CH₃NH₃PbI₃ (MAPbI₃) mixed with a small amount of CH₃NH₃PbCl₃ (MAPbCl₃) can be obtained after an annealing process at temperatures around 100 °C for 2 h. The synthesis of the obtained hybrid halide perovskites yields uniform films with reproducible properties. The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, UV–Vis spectroscopy and photoluminescence (PL). The XRD measurements confirm the presence of cubic CH₃NH₃PbCl₃ perovskite crystallites mixed with tetragonal perovskite crystallites of CH₃NH₃PbI₃ in the films with crystallite sizes for the latter around 34.8 nm. Texture analysis indicates that these crystallites have a preferential orientation at the (002) plane. Raman characterization shows the presence of PbI₂ and MAPbI₃ vibrational modes. Photoluminescence at room temperature shows an intense emission peak at 1.61 eV associated to the excitonic transition energy of the hybrid lead iodide perovskites. From optical transmittance measurements we notice that the absorption edge is around 1.61 eV, in good agreement with the photoluminescence results. This effective band gap energy is associated with a small amount of CH₃NH₃PbCl₃ (around 6%) mixed with CH₃NH₃PbI₃ crystallites. We are in the process of optimizing the photoelectronic and structural properties of the films for their application as inexpensive absorbing layers in solar cells.     

Effect of deposition time on optical, structural and photoluminescence properties of Cd0.6Co0.4S thin films by chemical bath deposition method

Cd_0.6Co_0.4S thin films have been deposited successfully on glass plates using chemical bath deposition method at 80° C by changing the time of deposition as a controlling parameter from 10 to 30 h. X-ray diffraction measurement shows the Co substitution of cadmium sulphide (CdS) system with hexagonal structure having the average crystalline between 1.79 and 2.13 nm. Energy dispersive X-ray spectrum reveals the presence of Co in the Cd–S lattice. The change in lattice parameters is demonstrated by the crystal size, bond length, micro-strain and the quantum confinement effect. The band gap energy is varied from 2.44 to 2.66 eV by changing the deposition times from 10 to 30 h which is useful to design a suitable window material in fabrication for solar cells. The presence of functional groups and the chemical bonding is confirmed by Fourier transform infrared spectra. The presence and the major blue shift of strong blue and red bands were demonstrated by photoluminescence spectra. The intensive emission properties of the Cd_0.6Co_0.4S thin films show a great potential for use as nano-scaled optoelectronic intensive light emitters under different deposition time.     

The effects of the aluminium concentration on optical and electrical properties of AZO thin films as a transparent conductive layer

In this paper, we studied the effects of the aluminium dopant concentration on the optical and electrical properties of aluminium doped zinc oxide (AZO) thin films grown on soda-glass substrates by a simple chemical method. The amount of aluminium in the compound was varied from 0 to 5 atomic percent (at.%), and the typical thickness of the films produced was about 300 nm. The thin films were characterized by scanning electron microscopy and X-ray diffraction to investigate the morphology and crystallinity of the samples. The optical properties of the thin films were studied by UV–Vis spectroscopy to determinate absorption, transmittance, and the diffuse reflectance. In addition, the photoluminescence properties of the thin films, excited with a 320 nm UV laser beam, were investigated. The effects of the aluminium concentration on these optical properties are discussed. The films with 2 and 5 % doping had excellent optical transmittance (~85–90 %) in the 400–1100 nm wavelength range. The photoluminescence spectra of the AZO films revealed UV near band edge emission peaks in the 378–401 nm range and an oxygen-vacancy related peak around 471 nm. The addition of aluminium changed the band gap of zinc oxide from 3.29 to 3.41 eV, and the appearance of a new level was observed in the band gap at the higher aluminium doping concentrations. The AZO thin films showed good conductivity (in the order of 10^?2 Ω cm) which allows their use as transparent electrodes. Moreover, the AZO thin films were stable in open air for 30 days.     

Structural,optical and magnetic properties of Ba and Ni doped CdS thin films prepared by spray pyrolysis method

Pure, Barium and Nickel doped cadmium sulphide (CdS) thin films have been coated on glass substrates at 400?°C by spray pyrolysis technique. The prepared CdS and doped CdS thin films were analysed by various measurements such as X-ray diffraction (XRD), SEM, optical and Vibrating Sample Magnetometer (VSM). X-ray diffraction measurements show that the coated pure, Ba and Ni-doped CdS thin films belong to the cubic crystal structure with orientation preferentially along (111) direction. The average crystallite size of pure, Ba and Ni doped CdS thin films were determined as 31, 33 and 45 nm, respectively. The average dislocation density (δ) and stacking fault (SF) of pure, Ba and Ni doped CdS thin films were also determined. The surface morphology and elemental analysis of the thin films were determined by scanning electron microscopy and energy dispersive X-ray spectrum (SEM with EDAX). It is observed that the optical energy bandgap has been decreased from 2.43 to 2.1 eV due to the doping Ba. The luminescence spectrum shows a strong emission peak at 517 nm in the case of pure CdS thin film and a meager red shift has been observed due to the doping. VSM studies were employed to study the magnetic behaviour of Ba and Ni doped CdS thin films.     

Blue shift in optical band gap of sol–gel derived Sn1−xZnxO2 polycrystalline thin films

Undoped and Zn doped SnO₂ thin films are deposited by sol–gel spin coating on glass substrate. XRD spectra with prominent peaks along (110) and (101) planes shows the polycrystalline nature of thin films. The particle size lies between 9.30 and 42.09 nm as estimated by Debye–Scherer method. SEM micrographs of the films contain pebble like structures spread throughout whose diameter decreases with increase in dopant concentration. Surface topology of the films is studied by atomic force microscopy. Transmission spectra show that all the films are highly transparent in the visible and IR spectral region (80–90 %) and a sharp absorption occurs near 300 nm. Approximately a change of 4 % is observed in the optical band gap by Zn doping. The optical band gap is tunable between 3.55 and 3.68 eV for 0 ≤ x ≤ 0.15 in nanocrystalline Sn_1?xZn_xO₂. Broad UV emission at 395 nm is observed in photoluminescence spectra of the films along with a blue emission. Emission intensity decreases as amount of Zn incorporated into SnO₂ increases.     

Structural characterization and frequency response of sol–gel derived Bi3/2MgNb3/2O7 thin films

The Bi_3/2MgNb_3/2O₇ (BMN) thin films were prepared via a modified sol–gel process on glass substrates at various post-annealing temperatures. The crystalline structure, morphology and frequency response have been investigated systematically. The X-ray diffraction results indicated that the BMN thin films had different orientations depending on post-annealing temperature. Thin films annealed above 650 °C presented well crystallized cubic pyrochlore structure with (222) orientation, and (400) preferentially oriented were observed when they were annealed below 600 °C. The surface morphology images of the BMN thin films revealed different grain size and grain size distribution, and the average grain size increased from 28.3 to 37.0 nm as the post-annealing temperature increasing. The low frequency dielectric properties of the BMN thin films were closely correlated with the (222) orientation, which was favorable to enhanced dielectric constant and tunability. The high-frequency optical measurements revealed an average transmittance (T _av ) varying between 76.6 and 82.2 % and band gap energy (E _g ) ranging from 3.40 to 3.44 as a function of the temperature and the crystallite size. Thin film annealed at 700 °C possessed the best crystallinity and highest (222) orientation, and showed the best electrical properties, with a dielectric constant of 105 at 1 MHz, dielectric tunability of 25.8 %, and an average optical transmittance of 82.2 % in the visible range (400–800 nm), making it promising for optical/electronic tunable devices applications.     

Cu content dependence of Cu<Subscript>2</Subscript>Zn(SnGe)Se<Subscript>4</Subscript> solar cells prepared by using sequential thermal evaporation technique of Cu/Sn/Cu/Zn/Ge stacked layers

The doping of Cu₂ZnSnSe₄ semiconductor with Ge element has demonstrated improvements to kesterite solar cell efficiency. However, the impact of different Cu concentrations on Cu₂ZnSnGeSe₄/CdS solar cell performance has been poorly studied. In this work, Cu₂ZnSnGeSe₄ thin films with different Cu contents were synthesized by selenization of sequential thermal evaporation precursors. Solar cells based on kesterite-type Cu₂ZnSnGeSe₄ (CZTGSe) were fabricated and the influence of the Cu thickness on the chemical composition and morphology of the layers and electro-optical properties of solar cells was studied. The stacking process was performed at room substrate temperature. Efficiency values in the range of 2.0–6.8% are reported as a function of Cu concentration. The highest efficiency of 6.8%, was achieved for solar cell with glass/Mo/CZTGSe/CdS/i-ZnO/ITO structure using the stacking of Cu (3 nm)/Sn (248 nm)/Cu (112 nm)/Zn (174 nm)/Ge (20 nm).     

Composition-dependent structural, optical and electrical properties of In x Ga1−x N (0.5 ≤ x ≤ 0.93) thin films grown by modified activated reactive evaporation

In this report, we have studied the compositional dependence of structural, optical and electrical properties of polycrystalline In _x Ga_1?x N thin films grown by modified activated reactive evaporation. The growth was monitored by optical emission spectroscopy. The thickness of the films was in the range ~600–800 nm. The phase, crystallinity and composition of the films were determined by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analysis. The surface morphology was studied by atomic force microscopy. The band gaps of these films obtained from transmittance and photoluminescence measurements were found to vary from 1.88 to 3.22 eV. All the films show n-type conductivity. The carrier concentration was found to be decreasing with increase in gallium incorporation which is in good agreement with the free carrier absorption observed in transmittance spectra.     

A study of the structural,optical, and electrical properties of SnS<Subscript>2</Subscript>:Cu optical semiconductor thin films deposited by the spray pyrolysis technique

Cu-doped tin-sulfide thin films were deposited onto glass substrates at T = 400 °C through spray pyrolysis. The effects of Cu doping on the structural, optical, and electrical properties of the thin films were investigated. The precursor solution was prepared by dissolving tin chloride (SnCl₄·5H₂O) and thiourea (CS(NH₃)₂) in deionized water and then adding copper chloride (Cl₂Cu₂H₂O). SnS₂:Cu thin films were prepared with \(\frac{{\left[ {Cu} \right]}}{{\left[ {Sn} \right]}}\% = 0, 1, 2, 3, 4 \,{\text{at}}.\%\). X-ray diffraction analysis showed that the thin films had a preferred (001) orientation of the SnS₂ phase and that the intensity of the (001) peak decreased with increased doping concentration from 1–4 at.%. Scanning electron microscopy studies indicated that the thin films had spherical grains. Characterization results of thin films showed that single-crystal grains, average grain size, optical band gap, carrier concentration, Hall mobility, and electrical resistance varied within 5–14 nm, 46–104 nm, 2.81–2.99 eV, 2.42 × 10¹⁶–26.73 × 10¹⁶ cm^?3, 2.41 × 10^?3–20.04 × 10^?3 cm²/v.s, and 9.05–12.89 Ω cm, respectively. Hall effect studies further revealed that the films exhibited n-type conductivity.     

Ferromagnetism in Gd-doped CdS dilute magnetic semiconducting nanorods

Cd _x Gd_1?x S (x = 0–0.15) nanorods have been synthesized by solvothermal technique. X-ray diffraction study reveals that pure and Gd-doped CdS nanorods exhibits hexagonal wurtzite structure. Transmission electron microscopy reveals nanorods like morphology of synthesized CdS having 14 and 26 nm size of pure and 15 % doped CdS nanorods. UV–Visible absorption study confirms the blue shift in the energy band energy due to the quantum confinement effects. Photoluminescence spectra confirm the defect free nature of the synthesized nanorods with peaks emerging around 528 and 540 nm due to the green emission. The magnetic study shows that the pure and Gd-doped CdS nanorods exhibits ferromagnetic character and the magnetisation increased by five times from 0.074 to 0.422 emu/g upon Gd-doping.     

Influence of the Cd/S Molar Ratio on the Optical and Structural Properties of Nanocrystalline CdS Thin Films

Nanocrystalline CdS thin films have been deposited using precursors with different thiourea concentrationonto glass substrates by sol-gel spin coating method.The crystalline nature of the films has been observedto be strongly dependent on thiourea concentration and annealing temperature.The CdS films are found tobe nanocrystalline in nature with hexagonal structure.The grain size is found to be in the range of 7.6 to11.5 nm depending on the thiourea concentration and annealing temperature.The high resolution transmissionelectron microscopy (HRTEM) results of the CdS films prepared using cadmium to thiourea molar ratio of0.3:0.3 indicate the formation of nanocrystalline CdS with grain size of 5 nm.Fourier transform infrared (FTIR)analysis shows the absorption bands corresponding to Cd and S.The optical study carried out to determinethe band gap of the nanostructured CdS thin films shows a strong blue shift.The band gap energy has beenobserved to lie in the range of 3.97 to 3.62 eV following closely the quantum confinement dependence ofenergy on crystallite radius.The dependence of band gap of the CdS films on the annealing temperature andthiourea concentration has also been studied.The photoluminescence (PL) spectra display two main emissionpeaks corresponding to the blue and green emissions of CdS.     

Nanocrystalline TiO2 thin films for NH3 monitoring: microstructural and physical characterization

Nanocrystalline titanium oxide thin films have been deposited by spin coating technique and then have been analyzed to test their application in NH₃ gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by X ray diffraction, Scanning microscopy, high resolution electron microscopy and selected area electron diffraction. The X-ray diffraction measurements confirmed that the films grown by this technique have good crystalline tetragonal mixed anatase and rutile phase structure. The HRTEM image of TiO₂ thin film showed grains of about 50–60 nm in size with aggregation of 10–15 nm crystallites. Selected area electron diffraction pattern shows that the TiO₂ films exhibited tetragonal structure. The surface morphology (SEM) of the TiO₂ film showed that the nanoparticles are fine with an average grain size of about 50–60 nm. The optical band gap of TiO₂ film is 3.26 eV. Gas sensing properties showed that TiO₂ films were sensitive as well as fast in responding to NH₃. A high sensitivity for ammonia indicates that the TiO₂ films are selective for this gas.     

Substrate temperature dependent physical properties of sprayed Zn0.76Mg0.24O films

The composition, microstructural and opto-electronic properties of Zn_1?x Mg _x O thin films grown by spray pyrolysis have been studied. The films were prepared on glass substrates at different substrate temperatures in the range, 200–350 °C for a fixed magnesium composition of x = 0.24. The films showed the predominant (002) reflection corresponding to the hexagonal wurtzite structure of ZnO. The preferred orientation doesn’t change with the deposition temperature. The films prepared at 300 °C showed good crystallinity with an average surface roughness of 6.2 nm. The optical studies revealed that the optical transmittance increased slightly with the increase of substrate temperature of the films. The variation of energy band gap, photoluminescence and electrical resistivity of the grown layers was also studied.     

Aqueous synthesis of CdSe and CdSe/CdS quantum dots with controllable introduction of Se and S sources

A new and convenient route is developed to synthesize CdSe and core–shell CdSe/CdS quantum dots (QDs) in aqueous solution. CdSe QDs are prepared by introducing H₂Se gas into the aqueous medium containing Cd²⁺ ions. The synthesized CdSe QDs are further capped with CdS to form core–shell CdSe/CdS QDs by reacting with H₂S gas. The gaseous precursors, H₂Se and H₂S, are generated on-line by reducing SeO₃ ^2? with NaBH₄ and the reaction between Na₂S and H₂SO₄, and introduced sequentially into the solution to form CdSe and CdSe/CdS QDs, respectively. The synthesized water-soluble CdSe and CdSe/CdS QDs possess high quantum yield (3 and 20 %) and narrow full-width-at-half-maximum (43 and 38 nm). The synthesis process is easily reproducible with simple apparatus and low-toxic chemicals. The relatively standard deviation of maxima fluorescence intensity is only 2.1 % (n = 7) for CdSe and 3.6 % (n = 7) for CdSe/CdS QDs. This developed route is simple, environmentally friendly and can be readily extended to the large-scale aqueous synthesis of QDs.