Synthesis and characterization of low particle size nanocrystalline SnSe thin films

Tin selenide (SnSe) nanocrystalline thin films of different thickness from 15 to 70 nm were prepared by inert gas condensation technique. Argon gas flow and substrate temperature were kept constant during deposition process at 2 × 10^?3 Torr and 27 °C respectively. Polycrystalline orthorhombic phase structured was deduced for the prepared SnSe ingot powder by X-ray diffraction pattern. The grazing incident in-plane X-ray diffraction (GIIXD) pattern showed nanocrystalline orthorhombic structure for deposited SnSe thin film. The TEM micrographs showed that thin films were nanocrystalline with particle size in the range from 2 to 5.7 nm. The optical band gap E_g of the thin films due to direct allowed transition have values ranging from 2.5 to 2.13 eV as the particle size increases from 2 to 5.7 nm. The photoconductivity spectra of the nanostructured SnSe thin films of different particle size showed transitions at 2.45, 2.34 and 2.21 eV for films of different particle size.     

CdS quantum dot sensitized nanocrystalline Gd-doped TiO2 thin films for photoelectrochemical solar cells

CdS quantum dot sensitized Gd-doped TiO₂ nanocrystalline thin films have been prepared by chemical method. X-ray diffraction analysis reveals that TiO₂ and Gd-doped TiO₂ nanocrystalline thin films are of anatase phase. The absorption spectra revealed that the absorption edge of CdS quantum dot sensitized Gd-doped TiO₂ thin films shifted towards longer wavelength side (red shift) when compared to that of CdS quantum dot sensitized TiO₂ films. CdS quantum dots with a size of 5 nm have been deposited onto Gd-doped TiO₂ film surface by successive ionic layer adsorption and reaction method and the assembly of CdS quantum dot with Gd-doped TiO₂ has been used as photo-electrode in quantum dot sensitized solar cells. CdS quantum dot sensitized Gd-doped TiO₂ based solar cell exhibited a power conversion efficiency of 1.18 %, which is higher than that of CdS quantum dot sensitized TiO₂ (0.91 %).     

P-type conductivity in doped and codoped ZnO thin films synthesized by RF magnetron sputtering

N-doped and Al–N codoped ZnO thin films with different volume ratios of N₂ reactive gas were deposited on plane glass substrates using the radio frequency magnetron sputtering method. The phase transition temperature and absorption edge of the ZnO powder were studied by differential scanning calorimetry at different heating rates and with Fourier transform infrared spectroscopy, respectively. The target used for the sputtering was synthesized using a palletize machine. It was sintered at 450 °C for 5 h. The X-ray diffraction results confirm that the thin films have wurtzite hexagonal structures with a very small distortion. The results indicate that the ZnO thin films have obviously enhanced transmittance of up to 80% on an average in the visible region. The Al–N codoped ZnO thin films exhibited the best p-type conductivity with a resistivity of 0.825 Ω-cm, a hole concentration of 6.55 × 10¹⁹ cm^?3, and a Hall mobility of 1.25 cm²/Vs. The p-type conductivity was observed after doping and codoping of the ZnO thin film.     

Low indium content In–Zn–O system towards transparent conductive films: structure,properties and comparison with AZO and GZO

In this work, low content indium doped zinc oxide (IZO) thin films were deposited on glass substrates by RF magnetron sputtering using IZO ceramic targets with the In₂O₃ doping content of 2, 6, and 10 wt%, respectively. The influences of In₂O₃ doping content and substrate temperature on the structure and morphology, electrical and optical properties, and environmental stability of IZO thin films were investigated. It was found that the 6 wt% doped IZO thin film deposited at 150?°C exhibited the best crystal quality and the lowest resistivity of 9.87?×?10^?4 Ω cm. The corresponding Hall mobility and carrier densities were 9.20 cm² V^?1 s^?1 and 6.90?×?10²⁰ cm^?3, respectively. Compared with 2 wt% Al₂O₃ doped ZnO and 5 wt% Ga₂O₃ doped ZnO thin films, IZO thin film with the In₂O₃ doping content of 6 wt% featured the lowest surface roughness of 1.3 nm. It also showed the smallest degradation with the sheet resistance increased only about 4.4% at a temperature of 121?°C, a relative humidity of 97% for 30 h. IZO thin film with 6 wt% In₂O₃ doping also showed the smallest deterioration with the sheet resistance increased only about 2.8 times after heating at 500?°C for 30 min in air. The results suggested that low indium content doped ZnO thin films might meet practical requirement in environmental stability needed optoelectronic devices.     

Electrical,optical and magnetoresistive behavior of nanostructured ZnO:Cu thin films deposited by sputtering

Copper doped ZnO (ZnO:Cu) nanostructured films with magnetoresistive behavior were produced by growing ZnO/Cu/ZnO arrays at room temperature (RT) by the sputtering technique on corning glass substrates. The arrays were made with two electrical insulating ZnO films of 50 and 105 nm, and a Cu film of 5 nm, both materials were deposited at RT by the RF- and DC-sputtering technique, respectively. The processing method involves two stages that proceed in the course of the growth process, the main one is originated by the non-equilibrium regime of the sputtering technique, and the second is the diffusion-redistribution of the intermediate Cu film towards the neighborhood ZnO layers aided by the nanocrystalline films character. The influence of applying an additional annealing stage to the arrays in N₂ atmosphere at 250 and 350 °C by periods of 30 min were studied. The resistivity of the ZnO:Cu films can be varied from 0.0034 to 2.83 Ω-cm, corresponding to electron concentrations of 1.12?×?10²¹ and 7.85?×?10¹⁷ cm^?3 with carrier mobility of 1.6 and 2.8 cm²/V s. Measured changes on the magnetoresistance behavior of the films at RT were of ?R?~?3% for annealed samples with electron concentration of 1.12?×?10²¹ cm^?3. The X-ray diffraction measurements show that the films are comprised of nanocrystallites with dimensions between 13 and 20 nm in size with preferred (002) orientation. The transmittance of the films in the visible region was of 83% with an optical band gap of ~?3.3 eV for the low-resistivity samples.     

Enhanced acetone detection using Au doped ZnO thin film sensor

Zinc oxide (ZnO) thin films are prepared using sol–gel method for acetone vapor sensing. Zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) was taken as starting material and a stable and homogeneous solution was prepared in ethanol by deliquescing the zinc acetate and distinct amount of monoethanolamine as a stabilizing agent. The prepared solution was then coated on silicon substrates by spin coating method and then annealed at 650 °C for preparing ZnO thin films. The thickness of the film was maintained at 410 nm. The structural, morphological and optical studies were done for the synthesized ZnO thin films. The operating temperature and sensor response is considered to be an important parameter for the gas sensing behavior of any material. Therefore, the present study examined the effect of sensing behavior of 3% v/v gold (Au) doped ZnO thin films as a sensor. The response characteristics of 410 nm ZnO thin film for temperature ranging from 180 to 360 °C were determined for the acetone vapors. The reported study provides a significant development towards acetone sensors, where a very high sensitivity with rapid response and recovery times are reported with lowered optimal operating temperature as compared to bare ZnO nano-chains like structured thin films. In comparison to the bare ZnO thin films giving a response of 63 at an operating temperature of 320 °C, a much better response of 132.3 was observed for the Au doped ZnO thin films at an optimised operating temperature of 280 °C for a concentration of 500 ppm of acetone vapors.     

A study of crystallographic phases in non-stoichiometric (oxygen deficiency) indium oxide thin films

Indium oxide is a well-known transparent conductive oxide (TCO) in its stoichiometric composition (In₂O₃). Its electrical and optical properties are strongly influenced by the chemical composition. This work focuses on an experimental investigation of the crystallographic phases in non-stoichiometric (oxygen deficiency) compositions of indium oxide thin films. The thin films were deposited at 300 °C by reactive sputtering of pure indium target at different oxygen gas flow rates on Si substrates. Two different phases are identified only in the non-stoichiometric compositions: metallic indium- and crystalline indium-rich oxide. The metallic indium phase appears as nano-crystals, a few nano-meters in diameter, evenly dispersed and occupies only 1 vol. % of the film. These metallic nano-particles have a negligible effect on the optical transparency and electrical conductivity of the films. The indium-rich oxide (In_xO_y) phase which occupies about 99 vol. % of the film has the bixbyite crystallographic structure and average grain size of about 50 nm. This phase has a pronounced effect on improving the TCO figure-of-merit (FM) relative to stoichiometric crystalline In₂O₃ films due to a higher increase of the electrical conductivity than the decrease of the optical transparency.     

Sputtering pressure dependent composition and dielectric properties in Bi1.5MgNb1.5O7 thin films deposited at room temperature by RF magnetron sputtering

Bismuth magnesium niobate (Bi_1.5MgNb_1.5O₇, BMN) thin films with cubic pyrochlore phase and a highly [111] orientation were deposited by radio frequency magnetron sputtering at different pressures and crystallized at 700 °C in oxygen atmosphere. For low temperature deposition, the sputtering pressure has significant influence on the surface roughness and composition of the BMN thin film. The film deposited at 4.0 Pa has the closest stoichiometric composition and a lowest surface roughness, which exhibits large dielectric constant and low dielectric loss (158 and 0.0046 at 1 MHz, respectively). The dielectric tunability and the figure of merit (FOM) value are 16.4 % and 36 at a dc bias field of 0.8 MV/cm. The relative large dielectric constant, low dielectric loss, and high FOM value suggest that BMN thin films have potential application for tunable microwave device.     

Opto-structural and electrical properties of chemically grown Ga doped MoBi2Se5 thin films

An arrested precipitation route was developed to obtain gallium doped MoBi₂Se₅ thin films on substrate support. High purity organometallic complexes of Mo–triethanolamine (Mo–TEA), Bi–triethanolamine (Bi–TEA), Ga–triethanolamine (Ga–TEA) allow to react with sodium selenosulphite (Na₂SeSO₃) in the presence of sodium dithionite (Na₂S₂O₄) as a reducing agent in an aqueous alkaline reaction bath. As deposited thin films were characterized by X-ray diffraction, which reveals that material is nanocrystalline with mixed phases of rhombohedral (Bi₂Se₃)-hexagonal (MoSe₂)-hexagonal (GaSe) structures. Scanning electron micrographs show the grain of granular morphology decreases with increase in Ga concentration. Energy dispersive x-ray analysis shows presence of Mo, Bi, Ga and Se elements in stoichiometric ratio confirms the chemical formula MoBiGaSe₅. Optical absorbance of the films show direct allowed transition in visible region having band gap energy in the range of 1.30–1.47 eV. Thermoelectric power and electrical conductivity measurements have been carried out for thin film samples in the temperature range 300–500 K and results revealed that n-type semiconducting behavior. It is interesting to note that Ga doping in MoBi₂Se₅ changes n to p type conductivity.     

Growth and properties of HfxZn1−xO thin films on flexible PET substrate using pulsed laser deposition

Hf-doped ZnO thin films with different Hf contents of target (Hf_xZn_1?xO 0 ≤ x ≤ 10 at.%) were deposited on flexible PET substrates under different oxygen pressure using pulsed laser deposition. Microstructures, optical and electrical properties of the films were studied. The results show that the as-deposited Hf_xZn_1?xO (0 ≤ x ≤ 5 at.%) films crystallized in ZnO hexagonal wurtzite structure with a highly preferred c-axis orientation. The films exhibited a transmission of higher than 80 % in the visible region. With increasing Hf content, the lattice constants increased; the morphology of the films deteriorated. The sheet resistance reached a minimum value of 16 Ω/□ when the doping level was about 0.5 at.%.     

Optical characterization of ZnO thin films deposited by Sol-gel method

In this paper, ZnO thin film is deposited on Pt/TiO₂/SiO₂/Si substrate using the sol-gel method and the effect of annealing temperature on the structural morphology and optical properties of ZnO thin films is investigated. The ZnO thin films are crystallized by the heat treatment at over 400°C. The ZnO thin film annealed at 600°C exhibits the greatest c-axis orientation and the Full-Width-Half-Maximum (FWHM) of X-ray peak is 0.4360°. A dense ZnO thin film is deposited by the growth of uniform grains with the increase of annealing temperature but when the annealing temperature increases to 700°C, the surface morphology of ZnO thin film becomes worse by the aggregation of ZnO particles. In the results of surface morphology of ZnO thin film using atomic force microscope (AFM), the surface roughness of ZnO thin film annealed at 600°C is smallest, that is, approximately 1.048 nm. For the PL characteristics of ZnO thin film, it is observed that ZnO thin film annealed at 600°C exhibits the greatest UV (ultraviolet) exciton emission at approximately 378 nm, and the smallest visible emission at approximately 510 nm among ZnO thin films annealed at various temperatures. It is deduced that ZnO thin film annealed at 600°C is formed most stoichiometrically, since the visible emission at approximately 510 nm comes from either oxygen vacancies or impurities.     

Intrinsic defects and structural phase of ZnS nanocrystalline thin films: effects of substrate temperature

Fabrications of ZnS nanocrystalline thin films at different substrate temperatures (T_S) of 200, 300 and 400 °C by means of pulsed laser deposition are presented. Thin film deposited at T_S of 200 °C is in cubic zinc-blende (ZB) structure while those deposited at T_S of 300 and 400 °C are in hexagonal wurtzite (W) phase. The grain size, surface roughness and bandgap of the films increases with increasing T_S. The zinc vacancies and interstitials in the films increases while sulfur vacancies decreases with increasing T_S. The variation of zinc and sulfur vacancies in ZnS films with T_S is responsible for structural phase transition from ZB to W which causes the change in energy bandgap.     

High quality ZnO:Al thin films deposited by using initial sputtering condition

High quality ZnO:Al (AZO) thin films sputtered at room temperature were deposited under a various initial pressures and its properties were investigated. With decreasing initial pressures, the crystallinity and sheet resistance of AZO thin films were improved and decreased, respectively. According to the composition results with the initial pressure, the low initial pressure promoted stoichiometric composition and increased Al composition in AZO thin films, resulting in improvement of crystallinity and increase of carrier concentration. These phenomena were attributed to reduction of residual gases with decreasing initial pressure. All samples exhibited highly transparent over 80 % at visible wavelength range (400–800 nm). In AZO thin films deposited at room temperature, the initial pressure is known to be a critical factor to obtain a high-quality thin film.     

Comparative study of multilayered ZnO/TiO<Subscript>2</Subscript>/ZnO and TiO<Subscript>2</Subscript>/ZnO/TiO<Subscript>2</Subscript> thin films prepared by sol–gel dip coating method

The aim of this research work is to represent the comparative study of ZnO/TiO₂/ZnO (ZTZ) and TiO₂/ZnO/TiO₂ (TZT) thin films deposited by sol–gel dip coating on FTO substrates. After deposition, the films were annealed at 500 °C for 1 h. Structural, surface morphology, optical and electrical properties of these films were studied by X-ray diffractrometer (XRD), Raman spectra, atomic force microscope (AFM), photoluminescence spectra (PL) and four point probe technique respectively. XRD and Raman spectra confirmed the anatase, brookite phases of TiO₂ and cubic phase of ZnO. AFM confirmed the formation of nano particles with average sizes of 18.4 and 47.2 nm of TZT and ZTZ films respectively. According to PL spectra, both the multilayer films slowdown the electron hole recombination rate and enhances the optoelectronic properties of the materials. Also it showed the peaks in the visible region of spectrum. The four point probe results showed that the average sheet resistivity of the films is 450 and 120 (ohm-m) respectively.     

A novel route for synthesis, characterization of molybdenum diselenide thin films and their photovoltaic applications

Molybdenum diselenide thin films were deposited by chemical method. The precursor solution contains ammonium molybdate, sodium selenosulphite with hydrazine hydrate as a reducing agent. Various preparative conditions were optimized for the formation of thin films. The X-ray diffraction pattern shows that thin films have a layer-hexagonal phase. EDAX analysis shows that the films are nearly stoichiometric of Mo: Se: 1:2. Optical properties show a direct band gap nature with band gap energy 1.43 eV and having specific electrical conductivity in the order of 10^?5 (Ωcm)^?1. The configuration of fabricated cell is n-MoSe₂ | NaI (2 M) + I₂ (1 M) | C (graphite). The photoelectrochemical characterization of the films is carried out by studying current–voltage characterization, capacitance–voltage and power output characteristics. The fill factor and efficiency of the cell were found to be 34.22 and 1.01 % respectively.     

Structural,morphological and optical properties of undoped and Co-doped ZnO thin films prepared by sol–gel process

Undoped and Co-doped ZnO thin films with different amounts of Co have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, isopropanol and monoethanolamine (MEA) were used as a precursor, doping source, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L^?1. The Co dopant level was defined by the Co/(Co + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis), photoluminescence (PL) and Raman. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found is 23.5 nm for undoped film. The results of SEM indicate that the undoped ZnO thin film has smooth and uniform surface with small ZnO grains, and the doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The average transmittance of all films is about 72–97 % in the visible range and the band gap energy decreased from 3.28 to 3.02 eV with increase of Co concentration. DRX, EDX and optical transmission confirm the substitution of Co²⁺ for Zn²⁺ at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show prominent mode representative of Zn_yCo_3?yO₄ secondary phase at larger values of Co concentration. PL of the films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity.     

Electrical characterization of nanocrystalline SnSe and ZnSe thin films: effect of annealing

In this paper, experimental data on the electrical properties of as deposited and annealed nanocrystalline SnSe and ZnSe thin films are reported. The thin films of SnSe and ZnSe are deposited on glass substrate by chemical bath deposition method. The films are studied before and after thermal annealing at temperatures 473 K for 1 h. This annealing is done in vacuum of 2?×?10^?3 mbar. The various electrical parameters like dark conductivity, photoconductivity, activation energy, photosensitivity and carrier life time have been measured on these films before and after annealing.     

Effect of very low to high Sb-doping on the structural,electrical, photo-conductive and thermoelectric properties of fluorine-doped SnO<Subscript>2</Subscript> (FTO) thin films prepared by spray pyrolysis technique

Transparent conducting fluorine and Sb-doped [SnO₂: (F, Sb)] thin films have been deposited onto preheated glass substrates using the spray pyrolysis technique by the various dopant quantity of spray solution. The effect of antimony impurities on the structural, morphological, electrical, Thermo-electrical, optical and photoconductive properties of films has been investigated. The [F/Sn] atomic concentration ratio (x) in the spray solution is kept at value of 0.7 and the [Sb/Sn] atomic ratio (y) varied at values of 0, 0.0005, 0.001, 0.002, 0.01, 0.03, 0.05, 0.07 and 0.10. It is found that the films are polycrystalline in nature with a tetragonal crystal structure corresponding to SnO₂ phase having orientation along the (110) and (200) planes. SEM images indicated that nanostructure of the films has a particle type growth. The average grain size increases with increasing spraying quantity of Sb-dopant. The compositional analysis of SnO₂: (F, Sb) thin films were studied using EDAX. SEM and AFM study reveals the surface of SnO₂: (F, Sb) to be made of nanocrystalline particles. The Hall Effect measurements have shown n-type conductivity in all deposited films. The lowest sheet resistance and highest the carrier concentration about 7.7 Ω/□ and 6.6 × 10²², respectively, were obtained for the film deposited with y = [Sb/Sn] = 0.001 and x = [F/Sn] = 0.7. The maximum of the Seebeck coefficient equal to 12.8 μV K^?1 was obtained at 400 K for the film deposited with y = [Sb/Sn] = 0.10. The average transmittance of films varied over the range 10–80 % with change of Sb-concentration. The band gap values of samples were obtained in the range of 3.19–3.8 eV. From the photoconductive studies, the Sb-doped films exhibited sensitivity to incident light especially in y = 0.001. The electrical resistivity and carrier concentration vary in range 5.44 × 10^?4 to 1.02 × 10^?2Ω cm and 2.6 × 10²²–6.6 × 10²² cm^?3, respectively.     

Structural and optical properties of ZnO films grown on silicon and their applications in MOS devices in conjunction with ZrO<Subscript>2</Subscript> as a gate dielectric

Photoluminescence (PL) properties of undoped ZnO thin films grown by rf magnetron sputtering on silicon substrates have been investigated. ZnO/Si substrates are characterized by Rutherford backscattering (RBS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). ZrO₂ thin films have been deposited on ZnO using microwave plasma enhanced chemical vapour deposition at a low temperature (150°C). Using metal insulator semiconductor (MIS) capacitor structures, the reliability and the leakage current characteristics of ZrO₂ films have been studied both at room and high temperatures. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Good electrical and reliability properties suggest the suitability of deposited ZrO₂ thin films as an alternative as gate dielectric on ZnO/n-Si heterostructure for future device applications.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.