Influence of oxygen partial pressure on electrical and optical properties of Zn0.93Mn0.07O thin films

The Zn_1−xMn_xO (x = 0.07) thin films were grown on glass substrates by direct current reactive magnetron cosputtering. The influence of oxygen partial pressure on the structural, electrical and optical properties of the films has been studied. X-ray-diffraction measurement revealed that all the films were single phase and had wurtzite structure with c-axis orientation. The experimental results indicated that there was an optimum oxygen partial pressure where the film shows relative stronger texture, better nano-crystallite and lower surface roughness. As the oxygen partial pressure increases, the carrier concentration systematically decreases and photoluminescence peaks related to zinc interstitials gradually diminish. The minimal resistivity of 70.48 Ω cm with the highest Hall mobility of 1.36 cm² V⁻¹ s⁻¹ and the carrier density of 6.52 × 10¹⁶ cm⁻³ were obtained when oxygen partial pressure is 0.4. All films exhibit a transmittance higher than 80% in the visible region, while the deposited films showed a lower transmittance when oxygen partial pressure is 0.4. With the increasing of oxygen partial pressure, the peak of near-band-edge emission has firstly a blueshift and then redshift, which shows a similar trend to the band gap in the optical transmittance measurement.     

Fabrication and characterization of ITO thin films on heat-resistant transparent flexible clay films

Transparent conductive indium tin oxide (ITO) thin films were deposited on transparent flexible clay films with heat resistant and high gas barrier properties by rf magnetron sputtering. The electrical, structural, and optical properties of these films were examined as a function of deposition temperature. A lowest resistivity of 4.2 × 10^− 4 Ωcm and an average transmittance more than 90% in the visible region were obtained for the ITO thin films fabricated at deposition temperatures more than 300 °C. It was found that ITO thin films with low resistivity and high transparency can be achieved on transparent flexible clay film using conventional rf magnetron sputtering at high temperature, those characteristics are comparable to those of ITO thin films deposited on a glass substrate.     

Conductive and transparent Bi-doped ZnO thin films prepared by rf magnetron sputtering

Bi-doped ZnO thin films were grown on glass substrates by ratio frequency (rf) magnetron sputtering technique and followed by annealing at 400 °C for 4 h in vacuum (~ 10^− 1 Pa). The effect of argon pressure on the structural, optical, and electrical properties of the Bi-doped films were investigated. The XRD patterns show that the thin films were highly textured along the c-axis and perpendicular to the surface of the substrate. Some excellent properties, such as high transmittance (about 85%) in visible region, low resistivity value of 1.89 × 10^− 3 W cm and high carrier density of 3.45 × 10²⁰ cm^− 3 were obtained for the film deposited at the argon pressure of 2.0 Pa. The optical band gap of the films was found to increase from 3.08 to 3.29 eV as deposition pressure increased from 1 to 3 Pa. The effects of post-annealing treatments had been considered. In spite of its low conductivity comparing with other TCOs, Bi-doping didn't appreciably affect the optical transparency in the visible range of ZnO thin films.     

Low temperature sputter deposition of SnOx:Sb films for transparent conducting oxide applications

SnO_x:Sb films have been prepared by reactive dc magnetron sputtering from a metallic target, with the aim of evaluating the potential of SnO_x:Sb as an attractive low-cost alternative to In₂O₃:Sn (ITO) for TCO applications. The deposition was performed without any additional heating of the substrates. The films were subsequently analysed regarding their optical, electrical and structural properties. Our results show that there is only a narrow process window for the sputter deposition of transparent and conducting tin oxide films at low temperature. A sharp minimum in resistivity of 4.9 mΩ cm is observed at an oxygen content of approximately 17% in the sputtering gas. Under these deposition conditions, the SnO₂:Sb films turn out to be both highly transparent and crystalline. At lower oxygen content (10-15%) the SnO_x:Sb films are substoichiometric, as revealed by Rutherford backscattering, and show a low transmission and high resistivity due to numerous defects and the presence of the SnO phase. At higher oxygen content (> 17%) excess oxygen is incorporated into the films, which is attributed to an increase of oxygen ion bombardment. This leads to a degradation of the electrical properties and a decrease of the density of the films, whilst the optical transmittance slightly improves.     

A study on crystallization, optical and electrical properties of the advanced ZITO thin films using co-sputtering system

Multi-functions (conductor, semiconductor and insulator) ZnInSnO (ZITO) transparent oxide thin films have been obtained by a co-sputtering system using ITO target and ZnO target with oxygen gas contents (0-8%). The ZITO film containing a small ITO content had the lowest resistivity (good electron mobility) and higher optical transmittance. In addition, the influences of thermal treatments (post-annealing and substrate temperature) on electrical properties and optical transmittance of ZITO films were studied. Photoluminescence (PL) of the ZITO film confirmed the contribution of ITO content and oxygen gas content on the photo-emission. The ZITO film with zinc atomic concentration of 58 at.% was a good candidate for TCO material (3.08 × 10⁻⁴ Ω cm). Under the substrate temperature of 100 °C or post-annealing temperature of 200 °C, the properties of ZITO film could be improved.     

Nickel-lithium oxide alloy transparent conducting films deposited by spray pyrolysis technique

In this research, nickel oxide (NiO) transparent semiconducting films are prepared by spray pyrolysis technique on glass substrates. The effect of Ni concentration in initial solution and substrate temperature on the structural, electrical, thermoelectrical, optical and photoconductivity properties of NiO thin films are studied. The results of investigations show that optimum Ni concentration and suitable substrate temperature for preparation of basic undoped NiO thin films with p-type conductivity and high optical transparency is 0.1 M and 450 °C, respectively. Then, by using these optimized deposition parameters, nickel-lithium oxide ((Li:Ni)O_x) alloy films are prepared. The XRD structural analysis indicate the formation of the cubic structure of NiO and (Li:Ni)O_x alloy films. Also, in high Li doping levels, Ni₂O₃ and NiCl₂ phases are observed. The electrical measurements show that the resistance of the films decreases with increasing Li level up to 50 at%. For these films, the optical band gap and carrier concentration are obtained to be 3.6 eV and 10¹⁵-10¹⁸ cm⁻³, respectively.     

Structural, optical and electrical properties of In-doped Cd2SnO4 thin films by spray pyrolysis method

Preparation of highly conducting and transparent In-doped Cd₂SnO₄ thin film by spray pyrolysis method at a substrate temperature of 525 °C is reported. In-doping concentration is varied between 1 and 5 wt.%. The effect of In-doping on structural, optical and electrical properties was investigated using different techniques such as X-ray diffraction, atomic force microscopy, optical transmittance and Hall measurement. X-ray diffraction studies revealed that the films are polycrystalline with cubic crystal structure. The undoped and In-doped Cd₂SnO₄ films exhibit excellent optical transparency. The average optical transmittance is ∼87% in the visible range for 3 wt.% In-doping. Further In-doping widens the optical band gap from 2.98 ± 0.1 eV to 3.04 ± 0.1 eV. A minimum resistivity of 1.76 ± 0.2 × 10⁻³ Ω cm and maximum carrier concentration of 9.812 ± 0.4 × 10¹⁹ cm⁻³ have been achieved for 1 wt.% In-doping in Cd₂SnO₄ thin films.     

P-type transparent conducting SnO2:Zn film derived from thermal diffusion of Zn/SnO2/Zn multilayer thin films

Highly transparent, p-type conducting SnO₂:Zn thin films are prepared from the thermal diffusion of a sandwich structure of Zn/SnO₂/Zn multilayer thin films deposited on quartz glass substrate by direct current (DC) and radio frequency (RF) magnetron sputtering using Zn and SnO₂ targets. The deposited films were annealed at various temperatures for thermal diffusion. The effect of annealing temperature and time on the structural, electrical and optical performances of SnO₂:Zn films was studied. XRD results show that all p-type conducting films possessed polycrystalline SnO₂ with tetragonal rutile structure. Hall effect results indicate that the treatment at 400 °C for 6 h was the optimum annealing parameters for p-type SnO₂:Zn films which have relatively high hole concentration and low resistivity of 2.389 × 10¹⁷ cm^− 3 and 7.436 Ω cm, respectively. The average transmission of the p-type SnO₂:Zn films was above 80% in the visible light range.     

Effects of thermal treatment on the characteristics of boron and tantalum-doped ZnO thin films deposited by the electrospraying method at atmospheric pressure

Metal-doped (B and Ta) ZnO thin films were deposited by the electrospraying method onto a heated glass substrate. The structural, electrical and optical properties of the films were investigated as a function of dopant concentration in the solution and also as a function of annealing temperature. The results show that all the prepared metal-doped ZnO films were polycrystalline in nature with a (0 0 2) preferred orientation. As the amounts of dopant were increased in the starting solution, the crystallinity and transmittance decreased. On the other hand, heat treatment of the films enhanced the transmittance, Hall mobility, carrier concentration and crystallinity. It was also observed that 2 at.% is the optimal doping amount in order to achieve the minimum resistivity and maximum optical transmittance. As-deposited films have high resistivity and low optical transmittance. The annealing of the as-deposited thin films in air resulted in the reduction of resistivity. Depending on the characteristics of dopant, mainly ionic radius, the effects of dopant were studied on the properties of ZnO thin films. Boron and tantalum have been considered as dopants, tantalum being the superior of the two, since it showed the lower resistivity and higher carrier concentration as well as higher mobility. The minimum value of resistivity was 1.95 × 10^− 4 Ω cm (15 Ω/□) with an optical transmittance more than 93% in the visible region and minimum resistivity of 2.16 × 10^− 4 Ω cm (18 Ω/□) with an optical transmittance greater than 96% for 2 at. % tantalum- and boron-doped ZnO films respectively. The present values of resistivities were closer to the indium tin oxide (ITO) resistivity and also closest to the lowest resistivity values among the ZnO films that were previously reported. The prepared films exhibit the good crystalline structure, homogenous surface, high optical transmittance and low resistivity that are preferable for optical devices.     

Sputter deposition and computational study of M-TiO2 (M = Nb, Ta) transparent conducting oxide films

Titanium dioxide (TiO₂) of the anatase phase has recently attracted much attention as a novel transparent conducting oxide (TCO) due to its rich availability, high refractive index with low absorption in the solar spectrum. While it has been found that Nb is a dopant to obtain low resistivity (~ 10^− 4 Ωcm), other metals such as Ta, W etc., are also considered as potential effective dopants. In this paper, we carried out a parallel study on Nb- and Ta-doped TiO₂ anatase films both theoretically by first principles calculation and experimentally by sputtering deposition and optical/electrical characterizations. The Nb-TiO₂ films deposited on glass by co-sputtering at room temperature were amorphous, and the films crystallized into an anatase structure after vacuum-annealing, with the measured resistivity values comparative to the reported. The Ta-TiO₂ films were deposited similarly, and the structure and properties were compared with the Nb-doped ones. Results showed that better performance was found in Nb-TiO₂ films than that in Ta-TiO₂ films. Theoretical calculations indicate that the larger lattice distortion by substitution of Ta for Ti is the dominating factor to suppress crystal growth and weaken the ability of electron mobility.     

Transparent p-type CuxS thin films

The effect of different mild post-annealing treatments in air, at 270 °C, for 4-6 min, on the optical, electrical, structural and chemical properties of copper sulphide (Cu_xS) thin films deposited at room temperature are investigated. Cu_xS films, 70 nm thick, are deposited on glass substrates by vacuum thermal evaporation from a Cu₂S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive crystalline CuS (covellite) films show high carrier concentration (∼10²² cm⁻³), low electrical resistivity (∼10⁻⁴ Ω cm) and inconclusive p-type conduction. After the mild post-annealing, these films display increasing values of resistivity (∼10⁻³ to ∼10⁻² Ω cm) with annealing time and exhibit conclusive p-type conduction. An increase of copper content in Cu_xS phases towards the semiconductive Cu₂S (chalcocite) compound with annealing time is reported, due to re-evaporation of sulphur from the films. However, the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice. In the most resistive films a Cu₂O phase is also observed, diminishing the amount of available copper to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%). The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper deficient in regards to the stoichiometric Cu₂S and exhibit stable p-type conductivity.     

New process for synthesis of ZnO thin films: Microstructural, optical and electrical characterization

Nanocrystalline ZnO thin films were prepared on glass substrates by using spin coating technique. The effect of annealing temperature (400-700 °C) on structural, compositional, microstructural, morphological, electrical and optical properties of ZnO thin films were studied by X-ray diffraction (XRD), Energy dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM), High Resolution Transmission Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Electrical conductivity and UV-visible Spectroscopy (UV-vis). XRD measurements show that all the films are nanocrystallized in the hexagonal wurtzite structure and present a random orientation. The crystallite size increases with increasing annealing temperature. These modifications influence the optical properties. The AFM analysis revealed that the surface morphology is smooth. The HRTEM analysis of ZnO thin film annealed at 700 °C confirms nanocrystalline nature of film. The SEM results shows that a uniform surface morphology and the nanoparticles are fine with an average grain size of about 40-60 nm. The dc room temperature electrical conductivity of ZnO thin films were increased from 10⁻⁶ to 10⁻⁵ (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of ZnO films annealed at 400-700 °C were estimated to be of the order of 4.75-7.10 × 10¹⁹ cm⁻³ and 2.98-5.20 × 10⁻⁵ cm² V⁻¹ S⁻¹.The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 3.32 eV to 3.18 eV with increasing annealing temperature between 400 and 700 °C. This means that the optical quality of ZnO films is improved by annealing.It is observed that the ZnO thin film annealing at 700 °C has a smooth and flat texture suited for different optoelectronic applications.     

Effects of Mg substitution on the structural, optical, and electrical properties of CuAlO2 thin films

Mg-doped CuAlO₂ thin films are prepared by the chemical solution method. The XRD results show that the solid solubility of Mg species on Al sites in CuAlO₂ lattice is lower than 2 at.%. When less than 2 at.% of Mg is added to the CuAlO₂ film, the surface roughness of the films was reduced with Mg substitution. Moreover, the c-axis orientation of the films improves because the in-plane fusion between CuAlO₂ crystallites is hindered. Optical and electrical measurements show that substituting Al³⁺ in the films with Mg²⁺ increases both their transmittance in the visible region and their optical band gaps. As well, their electrical conductivity is enhanced. At 300 K, the conductivity of the 1 at.% Mg-doped sample is up to 5.2 × 10⁻³ S/cm. Thus, Mg-doped CuAlO₂ films may have potential applications as transparent conductive oxides.     

Thin films of thermoelectric compound Mg2Sn deposited by co-sputtering assisted by multi-dipolar microwave plasma

Magnesium stannide (Mg₂Sn) thin films doped with Ag intended for thermoelectric applications are deposited on both silicon and glass substrates at room temperature by plasma assisted co-sputtering. Characterization by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction confirms the formation of fine-grained polycrystalline thin films with thickness of 1-3 μm. Stoichiometry, microstructure and crystal structure of thin films are found to vary with target biasing and the distance from targets to substrate. Measurements of electrical resistivity and Seebeck coefficient at room temperature show the maximum power factor of ∼5.0 × 10⁻³ W K⁻² m⁻¹ for stoichiometric Mg₂Sn thin films doped with ∼1 at.% Ag.     

Temperature driven evolution of thermal, electrical, and optical properties of Ti-Al-N coatings

Monolithic single phase cubic (c) Ti_1−xAl_xN thin films are used in various industrial applications due to their high thermal stability, which beneficially effects lifetime and performance of cutting and milling tools, but also find increasing utilization in electronic and optical devices. The present study elucidates the temperature-driven evolution of heat conductivity, electrical resistivity and optical reflectance from room temperature up to 1400 °C and links them to structural and chemical changes in Ti_1−xAl_xN coatings. It is shown that various decomposition phenomena, involving recovery and spinodal decomposition (known to account for the age hardening phenomenon in c-Ti_1−xAl_xN), as well as the cubic to wurtzite phase transformation of spinodally formed AlN-enriched domains, effectively increase the thermal conductivity of the coatings from ∼3.8 W m⁻¹ K⁻¹ by a factor of three, while the electrical resistivity is reduced by one order of magnitude. A change in the coating color from metallic grey after deposition to reddish-golden after annealing to 1400 °C is related to the film structure and discussed in terms of film reflectivity.     

Structural and optical study of samarium doped cerium oxide thin films prepared by electron beam evaporation

Samarium doped cerium oxide films were grown on the glass substrate using e-beam deposition technique and then characterized using different techniques: X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and UV-visible spectroscopy measurements. XRD analysis shows that all the films have cubic structure and the crystallite size decreases from 18 to 13 nm as the samarium (Sm) concentration increases. The FE-SEM images indicate that all the films have columnar growth. UV-visible measurements reflect that the films have high transparency (>80%) in the visible region. From the Raman spectra, we have observed two peaks at 466 and 565 cm⁻¹. The peak at 466 cm⁻¹ is assigned to the F_2g mode of cerium oxide (CeO₂) whereas the peak at 565 cm⁻¹ is due to the presence of the oxygen vacancies. The increase in the intensity of the peak at 565 cm⁻¹ indicates that the oxygen vacancy increases with Sm doping.     

Influence of indium doping on the properties of spray deposited CdS0.2Se0.8 thin films

Polycrystalline indium doped CdS_0.2Se_0.8 thin films with varying concentrations of indium have been prepared by spray pyrolysis at 300 °C. The as deposited films have been characterized by XRD, AFM, EDAX, optical and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of indium doping concentration. AFM studies reveal that the RMS surface roughness of film decreases from 34.68 to 17.76 with increase in indium doping concentration up to 0.15 mol% in CdS_0.2Se_0.8 thin films and further it increases for higher indium doping concentrations. Traces of indium in CdS_0.2Se_0.8 thin films have been observed from EDAX studies. The optical band gap energy of CdS_0.2Se_0.8 thin film is found to decrease from 1.91 eV to 1.67 eV with indium doping up to 0.15 mol% and increase after 0.15 mol%. The electrical resistivity measurement shows that the films are semiconducting with minimum resistivity of 3.71 × 10⁴ Ω cm observed at 0.15 mol% indium doping. Thermoelectric power measurements show that films exhibit n-type conductivity.     

Pulsed laser deposition of transparent ZnO/MgO multilayers

We report on the structural, optical and electrical properties of ZnO/MgO multilayers grown by pulsed laser deposition technique. The film thickness of ZnO sublayer (t_ZnO) was found to have great impact on the properties of ZnO/MgO multilayers. Investigations reveal the structural phase transition from wurtzite phase to cubic phase with corresponding decrease in ZnO thickness. The optical transmittance of the multilayers is over 80% in the visible region and there is a gradual shift of absorption edge towards a longer wavelength with corresponding increase in ZnO sublayer thickness. Two absorption bands at around 400 nm and 270 nm were observed in the transmission spectra of ZnO/MgO multilayers for similar ZnO and MgO layer thickness, which has been ascribed to phase separation to hexagonal and cubic phases. The calculated optical band gap E_g shows a widening from 3.51 eV to 6.23 eV with corresponding decrease in ZnO sublayer thickness from 100 nm to 23 nm, which in turn leads to an increase in resistivity in ZnO/MgO multilayers. These results provide important information for the design and modeling of ZnO/MgO optoelectronic devices due to their adjustable bandgap energies.     

Transparent conducting oxide films of heavily Nb-doped titania by reactive co-sputtering

Niobium-doped titania (TNO) films of various Nb content were deposited on glass and silicon substrates by reactive co-sputtering of Ti and Nb metal targets. Nb content in the TNO films was varied from 0 to ∼13 at.% (atomic percent), corresponding to Ti_1−xNb_xO₂ with x = 0-0.52, by modulating the Nb target power from 0 to 150 W (Watts). The influence of ion bombardment on the TNO films was investigated by applying an RF substrate bias from 0 to 25 W. The as-deposited TNO films were all amorphous and insulating, but after annealing at 600 °C for 1 h in hydrogen, they became crystalline and conductive. The annealed films crystallized into either pure anatase or mixed anatase and rutile structures. The as-deposited and the annealed films were transparent, with an average transmittance above 70%. Anatase TNO film (Ti_1−0.39Nb_0.39O₂) with Nb 9.7 at.% exhibited a dramatically reduced resistivity of 9.2 × 10⁻⁴ Ω cm, a carrier density of 6.6 × 10²¹ cm⁻³ and a carrier mobility around 1.0 cm² V⁻¹ s⁻¹. In contrast, the mixed-phase Ti_1−0.39Nb_0.39O₂ showed a higher resistivity of 1.2 × 10⁻¹ Ω cm. This work demonstrates that the anatase phase, oxygen vacancies, and Nb dopants are all important factors in achieving high conductivities in TNO films.     

Study of post annealing influence on structural, chemical and electrical properties of ZTO thin films

Zinc-Tin-Oxide (ZTO) thin films were deposited on glass substrate with varying concentrations (ZnO:SnO₂; 100:0, 90:10, 70:30 and 50:50 wt.%) at room temperature by flash evaporation technique. These deposited ZTO films were annealed at 450 °C in vacuum. These films were characterized to study the effect of annealing and addition of SnO₂ concentration on the structural, chemical and electrical properties. The XRD analysis indicates that crystallization of the ZTO films strongly depends on the concentration of SnO₂ and post annealing where annealed films showed polycrystalline nature. Atomic force microscopy (AFM) images manifest the surface morphology of these ZTO thin films. The XPS core level spectra of Zn(2p), O(1s) and Sn(3d) have been deconvoluted into their Gaussian component to evaluate the chemical changes, while valence band spectra reveal the electronic structures of these films. A small shift in Zn(2p) and Sn(3d) core level towards higher binding energy and O(1s) core level towards lower binding energy have been observed. The minimum electrical resistivity (ρ ≈ 3.69 × 10⁻² Ω-cm), maximum carrier concentration (n ≈ 3.26 × 10¹⁹ cm⁻³) and Hall mobility (μ ≈ 5.2 cm² v⁻¹ s⁻¹) were obtained for as-prepared ZTO (50:50) film thereafter move towards lowest resistivity (ρ ≈ 1.12 × 10⁻³ Ω-cm), highest carrier concentration (n ≈ 2.96 × 10²⁰ cm⁻³) and mobility (μ ≈ 18.8 cm² v⁻¹ s⁻¹) for annealed ZTO (50:50) thin film.