Investigation of physico-chemical properties of conductive Ga-doped ZnO thin films deposited on glass and silicon wafers by RF magnetron sputtering

We report on the physico-chemical properties of Undoped and Ga-doped ZnO films fabricated on glass and p-Silicon wafers at room temperature by RF magnetron sputtering using a ZnO and Ga₂O₃ mixture raw powder target without sintering procedure. X-ray diffraction (XRD) and energy dispersion spectroscopy (EDS), scanning electronic microscopy, Raman scattering, ultraviolet–visible spectroscopy, photoluminescence (PL), Hall effect and impedance spectroscopy technique have been applied for the comparative study of ZnO and ZnO:Ga thin films. XRD and Raman studies have shown that the deposited films have a preferred orientation growth with Ga atoms both in substitutional and interstitial positions. EDS analyses have allowed to show that the metallic Ga atoms have been incorporated in the ZnO films. Doping by gallium resulted in a slight increase in the optical band gap energy of the films while the optical transmittance remains about 80 %. The PL analysis at room temperature revealed violet, blue, green and red emissions. Room temperature Hall measurements show that the lowest resistivity was 3.40 × 10^?4 Ω cm with an electron mobility of 18.56 cm²/V.s for an optimum Ga concentration of 4 wt%. Impedance spectroscopy study showed that σ_ac obeys the relation \(\sigma_{ac} = A\omega^{s}\). The exponent ‘‘s’’ was found to decrease with increasing the temperature. It is found that, the AC conductivity of all samples follow the correlated barrier hopping model. The Nyquist plots showed a single semicircle, indicating an equivalent circuit with a single parallel resistor R and capacitance C network. The values of the activation energy E _a deduced from both DC conductivity and relaxation frequency for all the studied samples ranged from 0.51 to 0.73 eV and the results are explained on the basis of the induced defects due to the addition of Ga into the ZnO films.     

Structural and optical properties of Cu2SnS3 and Cu3SnS4 thin films by successive ionic layer adsorption and reaction

Thin films of Cu₂SnS₃ and Cu₃SnS₄ were obtained by sulfurizing (Cu, Sn)S structured precursors prepared by successive ionic layer absorption and reaction method. The results of energy dispersive spectroscopy (EDS) indicate that some loss in Sn with increasing sulfurization temperature. For the sulfurization temperatures of 380, 400 and 500 °C, tetragonal (I-42m) Cu₂SnS₃, cubic (F-43m) Cu₂SnS₃ and tetragonal (I-42m) Cu₃SnS₄ were formed, respectively. The combination of X-ray diffraction (XRD) results and Raman spectroscopy reveals that there are small Cu_2?x S phase existing in the CTS thin films (400 and 500 °C). Scanning electron microscopy was used to study the morphology of the layers. The ternary compounds present a high optical absorption coefficient (>10⁴ cm^?1). The band gap energy (E _g ) of the CTS thin films is estimated by reflection spectroscopy. The ternary compounds present a high optical absorption coefficient (>10⁴ cm^?1). The estimated band gap energy (E _g ) is 1.05 eV for tetragonal (I-42m) Cu₂SnS₃, 1.19 eV for cubic (F-43m) Cu₂SnS₃, and 1.22 eV for tetragonal (I-42m) Cu₃SnS₄.     

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).     

Composition and structure of chemically deposited CulnSe2 thin films

The composition, morphology and crystallographic structure of CuInSe₂ films grown at 50°C and 90°C by the chemical method are discussed. Characterization includes EDS, X-ray and transmission electron diffraction and optical absorption spectroscopy. Nearly stoichiometric CuInSe₂ thin films are obtained with chalcopyrite structure and with thickness in the range 1–3 μm and the grain size in the range 0.2–1.5 μm, band gap near 0.9 eV and absorption coefficient α ≅ 10⁵ cm⁻¹.The effect of deposition mixture temperature on film orientation has been studied by X-ray and electron diffraction. Preferred orientation along [112] direction occurs at a deposition-mixture temperature of 90°C.     

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.     

Phase composition of selenized Cu2ZnSnSe4 thin films determined by X-ray diffraction and Raman spectroscopy

Thin layers of Sn onto Cu-Zn alloy with different component ratios were processed at different temperatures. Scrupulous comparative analyses were performed by room temperature Raman spectroscopy and X-ray-diffractometry. An excess of tin on the surface results in isothermal selenization at 450 °C in the hexagonal residuals of unstable SnSe₂ in the well-crystallized Stannite — Cu₂ZnSnSe₄. In similar selenization conditions, copper-rich layers as precursors result in the Stannite phase with micro-immersions of CuSe. Low-temperature photoluminescence spectra of selenized films indicated to two Gaussian shaped bands at 0.81 and 1.16 eV.     

Deposition of luminescent a-SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H Films with SiH<Subscript>4</Subscript>–N<Subscript>2</Subscript> gas mixture by VHF–PECVD using novel impedance matching method

Hydrogenated amorphous silicon nitride (a-SiN _x :H) films are produced from a SiH₄–N₂ gas mixture by plasma enhanced chemical vapor deposition (PECVD) system with a newly developed impedance matching method at frequencies 13.6–150 MHz. An increase in the rf power from 35 to 350 mW/cm² at the highest frequency of 150 MHz increases the optical bandgap (E _opt) from 2.0 to 4.5 eV. Optical emission spectroscopy (OES) of the SiH₄–N₂ plasma shows that the emission intensity of SiH* (414 nm) is almost proportional to deposition rate. Films of a-SiN _x :H deposited at 150 MHz and 210 mW/cm² has an optical bandgap of E _opt ≈ 4.1 eV and emits visible photoluminescence (PL) at room temperature (RT).     

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.     

Hot-injection synthesis and characterization of quaternary Cu2ZnSnSe4 nanocrystals

Cu₂ZnSnSe₄ (CZTSe) is one of promising materials in the use of absorber layers of solar cells. It contains earth-abundant elements of zinc and tin, a near-optimal direct band gap of ∼ 1.5 eV, as well as a large absorption coefficient ∼ 10⁴ cm-1. The CZTSe nanocrystals in oleylamine (OLA) was successfully prepared via hot-injection method. The characterization of its structure, composition, morphology and absorption spectra were done using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and UV-vis absorption spectra. The results revealed that the monodispersed nanocrystals were single phase polycrystalline within the range of 15-20 nm. Optical measurements showed a direct band gap of 1.52 eV, which was optimal for low cost solar cells. The capping property of OLA was also demonstrated by examining Fourier Transform Infrared Spectroscopy (FTIR) feature peaks of CZTSe and OLA, respectively.     

Effects of synthesis temperature on CuIn(S,Se)2 thin films prepared by one-step evaporation of Cu–In precursors

CuIn(S,Se)₂ thin films were grown on soda-lime glass substrates by one-step evaporation Cu–In precursors processes. Effects of synthesis temperature on the structural and optical properties of CuIn(S,Se)₂ absorption layers were studied. The changes of surface morphology among different samples were observed by field-emission scanning electron microscopy. From X-ray diffraction images and Raman spectra, the CuIn(S,Se)₂ films had good crystallinity quality when the synthesis temperature was 550 °C. The FWHM of (112) peaks decreased from 0.537° to 0.180°, and secondary phase Cu_x(S,Se) disappeared when the synthesis temperature increased from 300 to 550 °C. The Raman spectra of the films also showed the CuIn(S,Se)₂ A₁ mode peaks existed chalcopyrite, and the blue shift of the CuIn(S,Se)₂ A₁ mode peaks from 289 to 284 cm^?1. The optical properties of the films were showed by transmission spectra, and the energy band gap of the CuIn(S,Se)₂ thin films fabricated at 550 °C is 1.34 eV.     

Optical characterization of Cu2ZnSnSe4 grown by thermal co-evaporation

Cu₂ZnSnSe₄ thin films with different substrate temperature and Cu flux were grown by thermal co-evaporation. Raman scattering, photoluminescence, and contactless electroreflectance (ER) measurements were performed. The Raman spectra of Cu₂ZnSnSe₄ show two main peaks at 170 and 192 cm^− 1. The photoluminescence spectrum shows a peak below 1.0 eV. Franz-Keldysh oscillations (FKOs) were observed in the ER spectra. From the analysis of the FKOs, the bandgap energy of Cu₂ZnSnSe₄ thin films is estimated to be 1.07 eV at 90 K and 0.99 eV at room temperature. We conclude that the bandgap energy of Cu₂ZnSnSe₄ thin films is around 1.0 eV.     

Reaction pathway for synthesis of Cu<Subscript>2</Subscript>ZnSn(S/Se)<Subscript>4</Subscript> via mechano-chemical route and annealing studies

Reaction pathway for the formation of kesterite Cu₂ZnSn(S/Se)₄ (CZTS/Se) from elemental precursors (Cu, Zn, Sn, S/Se) has been investigated experimentally and is being reported in the current paper. To identify the various stages of reaction pathway and to identify the formation and consumption of secondary phases, X-ray diffraction and Raman spectroscopy tools were employed. A series of experiments for different ballmilling durations (5, 10, 15, 20, 25 and 30 h) were performed and the presence of different phases was recorded for each experiment. In addition to XRD and Raman studies, phase formation has also been confirmed using detailed XPS, TEM and SEM–EDS analysis. In addition, the effect of annealing temperature on composition and band gap of the CZTS/Se material has been discussed. Optical band gap of various samples of CZTS was observed in the range of 1.40–1.60 eV and that of CZTSe was observed in the range of 1.08–1.18 eV. The relatively simple, low cost, easily scalable mechanical alloying process along with understanding of reaction pathway will provide a future scope for bulk production of CZTS/Se absorber material for thin film solar cells.     

Defects and acceptor centers in ZnO introduced by C+-implantation

ZnO single crystals were implanted with 280 keV C⁺ to a dose of 6 × 10¹⁶ cm^?2. Positron annihilation measurements reveal a large number of vacancy clusters in the implanted sample. They further agglomerate into larger size or even microvoids after annealing up to 700 °C, and are fully removed at 1200 °C. X-ray diffraction, photoluminescence, and Raman scattering measurements all indicate severe damage introduced by implantation, and the damaged lattice is partially recovered after annealing above 500 °C. From room temperature photoluminescence measurements, an additional peak at around 3.235 eV appears in the implanted sample after annealing at 1100 °C, which is much stronger than that of the free exciton. From the analysis of low temperature photoluminescence spectra, this peak is mostly a free electron to acceptor (e,A⁰) line which is probably associated with C _O .     

Dependence of the properties of copper zinc tin sulfide thin films prepared by electrochemical deposition on sulfurization temperature

Copper zinc tin sulfide (CZTS, Cu₂ZnSnS₄) is a low band gap semiconductor that is attractive for use in solar cells. We investigated the dependence of the structure and properties of CZTS thin films on the temperature used to sulfurize precursor thin films composed of copper, zinc and tin fabricated by electrochemical deposition. The precursor films were sulfurized in a furnace with three zones, which allowed fine control of the sulfurization temperature between 250 and 400 °C. X-ray diffraction and Raman spectroscopic measurements confirmed that the films were composed of CZTS following sulfurization. The grain size and crystallinity of the films increased with sulfurization temperature. The composition of CZTS also varied with sulfurization temperature. The proportions of Cu and Zn increased while that of Sn decreased with increasing sulfurization temperature. Absorption and reflectance spectra revealed that the absorption coefficients and band gaps of the CZTS films varied with sulfurization temperature between 3–4.1 × 10⁴ cm^?1 and 1.4–1.53 eV, respectively. Solar cells containing CZTS sulfurized at 400 °C showed a maximum efficiency of 2.04 %, which was attributed to the higher crystallinity and larger grain size of CTZS compared with thin films sulfurized at lower temperatures. Our results show that control of sulfurization temperature is an important factor in optimizing the performance of CZTS thin films in solar cells.     

Influence of substrate temperature on the growth and properties of reactively sputtered In-rich InAlN films

Indium-rich InAlN films were prepared on Si (111) substrates by using reactive co-sputtering in a mixed Ar-N₂ atmosphere. The substrate temperature was varied from room temperature to 300 °C to investigate the film’s growth and properties at different temperatures. Structural and optical properties of the films were evaluated through high resolution XRD and Raman spectroscopy respectively, surface morphology and roughness analysis was performed by using FE-SEM and AFM respectively, whereas the electrical characterizations were made through resistivity and current–voltage (I–V) measurements respectively. Highly c-axis oriented nanocrystalline InAlN films with wurtzite structure were obtained at a substrate temperature of 100 °C and above. Structural quality of the films was improved with increase of the substrate temperature. The Raman spectroscopy revealed A₁ (LO) modes which became more intense by the increasing the substrate temperature. The electrical studies indicated n-type nature of InAlN film having electron concentration in the range 3 × 10¹⁹–20 × 10¹⁹ cm^?3. The electrical resistivity exhibited a decreasing trend with increase of the deposition temperature. The I–V measurements showed a noticeable increase in the value of current by increasing the substrate temperature to 300 °C.     

Effect of Co doping on the structure,optical and magnetic properties of LaAlO3 thin films

LaAl_1?x Co _x O₃ (x = 0, 0.05 and 0.10) thin films were fabricated on quartz substrates by sol–gel method. X-ray diffraction data indicate that all thin films belong to perovskite LaAlO₃, and there is no secondary phase. Two obvious Raman peaks are observed in the Raman spectra, and the 113 cm^?1 peak is assigned to A₁ mode of perovskite LaAlO₃ while the 696 cm^?1 peak is caused by the Co–O stretching vibration. The band gap of the films decreases from 5.66 to 5.40 eV with the Co composition increasing from 0 to 10 %. The magnetization of the films was investigated, and it enhances significantly with increase of the Co content.     

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.     

Selenization of electrodeposited copper–indium alloy thin films for solar cell applications

Copper–Indium (Cu–In) alloys with sulfur and selenium have technological importance in the development of thin film solar cell technology. We have used potentiostatic electrochemical technique with three-electrode geometry for the deposition of Cu–In alloy thin films in an aqueous electrolyte. Cathodic voltammetry (CV) was thoroughly studied to optimize the electrodeposition parameters. The deposition potential for Cu–In alloy was found to be in the range ?0.70 to ?0.85 V versus Ag/AgCl reference electrode. Polycrystalline Cu_xIn_y thin films were electrodeposited from aqueous bath at room temperature and 45 °C. Effect of concentration of citric acid was extensively studied by CV measurements. The as-deposited Cu–In films were characterized with a range of characterization techniques to study the structural, morphological, compositional and electrical properties. Thin layers of Cu–In were selenized in a homemade tubular furnace at 400 ^°C, which reveals the formation of polycrystalline CuInSe₂ (CISe) thin films with tetragonal structure. The band gap of CISe thin film was estimated ~1.05 eV by optical absorption spectroscopy. Nearly stoichiometric CISe thin film, Cu = 25.25 %, In = 26.48 % and Se = 48.27 % was obtained after selenization. The linear behavior of current density–voltage (J–V) was observed for Cu–In alloy thin films whereas, the selenized Cu–In alloy films (CISe) possess rectifying properties.     

Effect of stacking type in precursors on composition, morphology and electrical properties of the CIGS films

The copper-indium-gallium (CIG) metallic precursors with different stacking type (A: CuGa/CuIn/CuGa/glass and B: CuInGa/CuIn/CuInGa/glass) were prepared onto glass substrates by magnetron sputtering method. In order to prepare Cu(In_1?xGa_x)Se₂ (CIGS) thin films, the CIG precursors were then selenized with solid Se powder using a three-step reaction temperature profile. The influence of stacking type in precursors on structure, composition, morphology and electrical properties of the CIGS films is investigated by X-ray diffraction, energy dispersive spectrometer, scanning electron microscope and Hall effect measurement. The results reveal that the stacking type of the precursor has a strong influence on composition, morphology and properties of the CIGS thin films. The atomic ratios of Cu/(In+Ga)/Se of the CIGS films A and B are 1.61:1:2.11 and 1.39:1:2.04, respectively. The better quality CIGS thin films can be obtained through selenization of metallic precursor of CuInGa/CuIn/CuInGa/glass. The CIGS films are p-type semiconductor material. The hole concentration, resistivity and hole mobility of the CIGS thin films is 2.51 × 10¹⁷ cm^?3, 3.11 × 10⁴ Ω cm and 19.8 cm² V^?1 s^?1, respectively.     

Study on Mn-induced Jahn–Teller distortion in BiFeO3 thin films

Present work reports Raman spectroscopy study of single-phase Mn-doped BiFeO₃ [BiFe_1?x Mn _x O₃ (0 ≤ x ≤ 0.20)] polycrystalline thin films carried out in backscattering geometry. De-convolution of Raman spectra showed a gradual transition in the crystal symmetry from rhombohedral (?R) to multiphase [rhombohedral (?R) + tetragonal (?T)] structure with increasing Mn doping concentration in BiFe_1?x Mn _x O₃ (BFMO) thin films. X-ray diffraction (XRD) along with Le-Bail extraction refinement confirms that the structural symmetry lowering in BFMO thin films occurs at about 10 % Mn doping concentration. A blue shift is observed in the direct energy band gap of BFMO thin films from 2.53 to 2.87 eV (at T = 295 K) and is attributed to the local symmetry lowering and local induced strain in Fe³⁺ environment resulted from Jahn–Teller distortion in (MnFe)³⁺O₆ octahedral unit. Second-derivative analysis of FTIR spectra in the spectral regions (420–470) cm^?1 and (480–680) cm^?1 further indicates the favourable structure distortion leading to the simultaneous exhibition of enhanced ferromagnetic and ferroelectric properties owing to Mn substitution in host BiFeO₃ lattice.