Electrical and optical properties of Ga doped zinc oxide thin films deposited at room temperature by continuous composition spread

Ga doped ZnO (GZO) thin films were deposited on glass substrates at room temperature by continuous composition spread (CCS) method. CCS is thin films growth method of various Ga_xZn_1−xO(GZO) thin film compositions on a substrate, and evaluating critical properties as a function position, which is directly related to material composition. Various compositions of Ga doped ZnO deposited at room temperature were explored to find excellent electrical and optical properties. Optimized GZO thin films with a low resistivity of 1.46 × 10⁻³ Ω cm and an average transmittance above 90% in the 550 nm wavelength region were able to be formed at an Ar pressure of 2.66 Pa and a room temperature. Also, optimized composition of the GZO thin film which had the lowest resistivity and high transmittance was found at 0.8 wt.% Ga₂O₃ doped in ZnO.     

Characteristics of ZnO:Al thin films co-doped with hydrogen and fluorine

Fluorine and hydrogen co-doped ZnO:Al (AZO) films were prepared by radio frequency (rf) magnetron sputtering of ZnO targets containing 1 wt.% Al₂O₃ on Corning glass at substrate temperature of 150 °C with Ar/CF₄/H₂ gas mixtures, and the structural, electrical and optical properties of the as-deposited and the vacuum-annealed films were investigated. In as-deposited state, films with fairly low resistivity of 3.9-4 × 10⁻⁴ Ω cm and very low absorption coefficient below 900 cm⁻¹ when averaged in 400-800 nm could be fabricated. After vacuum-heating at 300 °C, the minimum resistivity of 2.9 × 10⁻⁴ Ω cm combined with low absorption loss in visible region, which enabled the figure of merit to uplift as high as 4 Ω⁻¹, could be obtained for vacuum-annealed film. It was shown that, unlike hydrogenated ZnO films which resulted in degradation upon heating in vacuum at moderately high temperature, films with fluorine addition could yield improved electrical properties mostly due to enhanced Hall mobility while preserving carrier concentration level. Furthermore, stability in oxidizing environment could be improved by fluorine addition, which was ascribed to the filling effect of dangling bonds at the grain boundaries. These results showed that co-doping of hydrogen and fluorine into AZO films with low Al concentration could be remarkably compatible with thin film solar cell applications.     

Influence of deposition temperature on morphological, optical, electrical and opto-electrical properties of highly textured nano-crystalline spray deposited CdO:Ga thin films

This study investigated the effect of deposition temperature on the morphological, optical, electrical and opto-electrical properties of CdO:Ga films prepared by a cost effective spray pyrolysis deposition method. The substrate temperature was varied from 275 to 375 °C, in steps of 25 °C. The XRD patterns reveal that films are polycrystalline with cubic structure and are highly textured along (2 0 0) preferential orientation. The crystallinity and crystallite size increases with deposition temperature. The SEM images confirmed these results and showed larger grains and more crystallization for the higher deposition temperature. The electrical studies show degenerate, n-type semiconductor nature with minimum resistivity of 1.93 × 10⁻⁴ Ω cm. Temperature dependence of electrical conductivity shows a semiconducting behavior with a spectrum of activation energy. The electrical conductivity of the film dependence of temperature shows the thermally activated band conduction mechanism. The optical gap varies from 2.54 to 2.74 eV. The highest figure of merit observed in the present study is 9.58 × 10⁻³ Ω⁻¹ and shows improvement than our previous reports. The blue shift of absorption edge (or bandgap widening BGW) can be described by the Moss-Burstein (M-B) effect in which the optical absorption edge of a degenerate n-type semiconductor is shifted towards higher energy.     

Effect of substrate temperature on the growth of ITO thin films

Indium tin oxide (ITO) thin films were deposited onto glass substrates by rf magnetron sputtering of ITO target and the influence of substrate temperature on the properties of the films were investigated. The structural characteristics showed a dependence on the oxygen partial pressure during sputtering. Oxygen deficient films showed (4 0 0) plane texturing while oxygen-incorporated films were preferentially oriented in the [1 1 1] direction. ITO films with low resistivity of 2.05 × 10⁻³ Ω cm were deposited at relatively low substrate temperature (150 °C) which shows highest figure of merit of 2.84 × 10⁻³ square/Ω⋅     

Growth of Ga-doped ZnO films with ZnO buffer layer by sputtering at room temperature

Gallium-doped zinc oxide films have been grown on glass substrates with and without ZnO buffer layers by r.f. magnetron sputtering at room temperature. In this approach, the grey relational Taguchi method analysis is adopted to solve the coating process with multiple deposition qualities. Optimal coating parameters can then be determined by using the gray relational grade as a performance index. The GZO coating parameters (r.f. power, sputtering pressure, O₂/(Ar+O₂) flow-rate ratios, and deposition time) are optimized, by taking into account the multiple performance characteristics (structural, morphological, deposition rate, electrical resistivity, and optical transmittance). The results indicate that with the grey relational Taguchi method, the electrical resistivity of GZO films is reduced from 9.23×10⁻³ to 5.77×10⁻³ Ω cm and optical transmittance increases from 79.42% to 82.95%, respectively. The ZnO buffer layer can reduce the electrical resistivity of GZO films from 5.77×10⁻³ to 2.38×10⁻³ Ω cm. It can be anticipated that room temperature deposition enables film deposition onto polymeric substrates for flexible optoelectronic devices.     

Influence of the grain boundary barrier height on the electrical properties of Gallium doped ZnO thin films

The pulsed laser deposition (PLD) technique is used to deposit Gallium doped zinc oxide (GZO) thin films on glass substrates at 250 with different Gallium (Ga) doping concentration of 0, 1.0, 3.0 and 5.0%. The influence of Ga doping concentration on structure, chemical atomic compositions, electrical and optical properties was investigated by XRD, XPS, Hall measurement and UV spectrophotometer, respectively. The relationship between electrical properties and Ga doping concentration was clarified by analyzing the chemical element compositions and the chemical states on the GZO films. It is found that the carrier concentrations and oxygen vacancies in the GZO films increase with increasing Ga doping concentration. The lowest resistivity (3.63 × 10⁻⁴ Ω cm) and barrier height of grain boundaries (14 mV) were obtained with 3% Ga doping. In particular, we suppose the band gap of 5% Ga doping sample larger than that of 3% Ga doping sample is due to the quantum size effect from the amorphous structure rather than Moss-Burstein shift.     

Fabrication and vacuum annealing of transparent conductive Ga-doped Zn0.9Mg0.1O thin films prepared by pulsed laser deposition technique

In this study, highly transparent conductive Ga-doped Zn_0.9Mg_0.1O (ZMO:Ga) thin films have been deposited on glass substrates by pulsed laser deposition (PLD) technique. The effects of substrate temperature and post-deposition vacuum annealing on structural, electrical and optical properties of ZMO:Ga thin films were investigated. The properties of the films have been characterized through Hall effect, double beam spectrophotometer and X-ray diffraction. The experimental results show that the electrical resistivity of film deposited at 200 °C is 8.12 × 10⁻⁴ Ω cm, and can be further decreased to 4.74 × 10⁻⁴ Ω cm with post-deposition annealing at 400 °C for 2 h under 3 × 10⁻³ Pa. In the meantime, its band gap energy can be increased to 3.90 eV from 3.83 eV. The annealing process leads to improvement of (0 0 2) orientation, wider band gap, increased carrier concentration and blue-shift of absorption edge in the transmission spectra of ZMO:Ga thin films.     

Substitution mechanism of Ga for Zn site depending on deposition temperature for transparent conducting oxides

High quality transparent conductive gallium-doped zinc oxide (GZO) thin films were deposited on glass substrates using rf-magnetron sputtering system at the temperature ranging from room temperature (RT) to 500 °C. The temperature-dependence of Ga doping effect on the structural, optical and electrical properties in ZnO has been investigated. For the GZO thin films deposited at over 200 °C, (103) orientation was strongly observed by X-ray diffraction analysis, which is attributed to the substitution of Ga elements into Zn site. X-ray photoelectron spectroscopy measurements have confirmed that oxygen vacancies were generated at the temperature higher than 300 °C. This might be due to the effective substitution of Ga³⁺ for Zn site at higher temperature. It was also found that the optical band gap increases with deposition temperature. The optical transmittance of GZO thin films was above 87% in the visible region. The GZO thin films grown at 500 °C showed a low electrical resistivity of 4.50 × 10^?4 Ω cm, a carrier concentration of 6.38 × 10²⁰ cm^?3 and a carrier mobility of 21.69 cm²/V.     

Femtosecond Z-scan measurement of third-order optical nonlinearities in anatase TiO2 thin films

Anatase phase TiO₂ films have been grown on fused silica substrate by pulsed laser deposition technique at substrate temperature of 750 °C under the oxygen pressure of 5 Pa. From the transmission spectra, the optical band gap and linear refractive index of the TiO₂ films were determined. The third-order optical nonlinearities of the films were measured by Z-scan method using a femtosecond laser (50 fs) at the wavelength of 800 nm. The real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ were determined to be −7.1 × 10⁻¹¹esu and −4.42 × 10⁻¹²esu, respectively. The figure of merit, T, defined by T=βλ/n₂, was calculated to be 0.8, which meets the requirement of all-optical switching devices. The results show that the anatase TiO₂ films have great potential applications for nonlinear optical devices.     

Preparation and multi-properties of insulated single-phase BiFeO3 ceramics

Six types of BiFeO₃ ceramic samples, with subtle differences in synthesis conditions, were prepared. The comparison of their phases, electrical resistivity, and porosity revealed that the use of Bi₂O₃ and Fe₂O₃ powders of <1 μm size and a rapid liquid-phase sintering process of 855 °C for 5 min at 100 °C/s is beneficial to synthesize poreless single-phase BiFeO₃ samples with high electrical resistivity of ∼5×10¹² Ω cm. Deoxygenated Bi_xFe_yO_{1.5x+1.5y−δ} (x≠y, δ≥0) impurities were identified and found to be the main cause of low electrical resistivity and high porosity in the multi-phase samples. Large saturation polarization of 16.6 μC/cm² and low leakage current density of 30 mA/m², both at a high electric field of 145 kV/cm, were measured in the optimized single-phase samples at room temperature besides a large piezoelectric d₃₃ coefficient of 27 pC/N and an obvious canted antiferromagnetic behavior.     

Effect of GZO thickness and annealing temperature on the structural,electrical and optical properties of GZO/Ag/GZO sandwich films

The GZO/Ag/GZO sandwich films were deposited on glass substrates by RF magnetron sputtering of Ga-doped ZnO (GZO) and ion-beam sputtering of Ag at room temperature. The effect of GZO thickness and annealing temperature on the structural, electrical and optical properties of these sandwich films was investigated. The microstructures of the films were studied by X-ray diffraction (XRD). X-ray diffraction measurements indicate that the GZO layers in the sandwich films are polycrystalline with the ZnO hexagonal structure and have a preferred orientation with the c-axis perpendicular to the substrates. For the sandwich film with upper and under GZO thickness of 40 and 30 nm, respectively, it owns the maximum figure of merit of 5.3 × 10⁻² Ω⁻¹ with a resistivity of 5.6 × 10⁻⁵ Ω cm and an average transmittance of 90.7%. The electrical property of the sandwich films is improved by post annealing in vacuum. Comparing with the as-deposited sandwich film, the film annealed in vacuum has a remarkable 42.8% decrease in resistivity. The sandwich film annealed at the temperature of 350 °C in vacuum shows a sheet resistance of 5 Ω/sq and a transmittance of 92.7%, and the figure of merit achieved is 9.3 × 10⁻² Ω⁻¹.     

A comparative study of the physical properties of Sb2S3 thin films treated with N2 AC plasma and thermal annealing in N2

As-deposited antimony sulfide thin films prepared by chemical bath deposition were treated with nitrogen AC plasma and thermal annealing in nitrogen atmosphere. The as-deposited, plasma treated, and thermally annealed antimony sulfide thin films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, UV-vis spectroscopy, and electrical measurements. The results have shown that post-deposition treatments modify the crystalline structure, the morphology, and the optoelectronic properties of Sb₂S₃ thin films. X-ray diffraction studies showed that the crystallinity of the films was improved in both cases. Atomic force microscopy studies showed that the change in the film morphology depends on the post-deposition treatment used. Optical emission spectroscopy (OES) analysis revealed the plasma etching on the surface of the film, this fact was corroborated by the energy dispersive X-ray spectroscopy analysis. The optical band gap of the films (E_g) decreased after post-deposition treatments (from 2.36 to 1.75 eV) due to the improvement in the grain sizes. The electrical resistivity of the Sb₂S₃ thin films decreased from 10⁸ to 10⁶ Ω-cm after plasma treatments.     

Dielectric behavior of spin-deposited nanocrystalline nickel-zinc ferrite thin films processed by citrate-route

Nanocrystalline nickel-zinc ferrite thin films with the general formula Ni_1−xZn_xFe₂O₄, where x=0.0, 0.2, 0.4 and 0.6 were fabricated via a chemical route known as the citrate precursor route. These films were spin-deposited on indium-tin oxide coated glass, fused quartz and amorphous Si-wafer substrates, and annealed at various temperatures up to 650 °C. The films annealed below 400 °C were found to be X-ray amorphous, while the films annealed at and above 400 °C were polycrystalline exhibiting a single-phase spinel structure. The average grain size of the films evaluated by transmission electron microscopy, is found to be in the range 4-8.5 nm. The room temperature DC resistivity of the films is in the range 10³-10⁷ Ω m. Dielectric constant and dielectric loss were measured in the frequency range 100 Hz-1 MHz. Dielectric constant of the films is found to lie between 25 and 44, while the loss factor is if the order of 10⁻². The higher values of the dielectric constant for films having higher zinc concentration are attributable to the enhanced hopping between Fe²⁺ and Fe³⁺ ions in these samples. The M-H hysteresis measurement of the nickel ferrite thin films annealed at 650 °C showed narrow hysteresis loop—a characteristic of soft ferromagnetic material.     

High resistive ferrite films by a solution process for electromagnetic compatible (EMC) devices

Mn-Zn ferrite films with high resistivity and good noise suppressing ability for use as ‘coupling-type noise suppressors’ have been prepared by the spin-spray ferrite plating. The as-prepared films were crystalline and exhibited single-phase spinel structure. The films had an ‘integrated nano-columnar’ morphology that resulted in a very high resistivity. Further, by varying the chemical composition, films with varying resistivity were prepared and then heat treated at 260 °C for 3 min, similar to that of the reflow soldering process. The reflection and transmission coefficients, S₁₁ and S₂₁ parameters, on coplanar micro-strip line (50 Ω) were measured for the as-prepared and heat-treated films in order to study the effect of heat treatment. When the resistivity was above 2×10⁵ Ω/sq, S₁₁ and S₂₁ exhibited uniform profiles throughout the measurement frequency (50 MHz-10 GHz), which is ideal for the ‘coupling-type’ noise suppressor. These films retain a moderately high resistivity and hence do not show the downshift in the stopband frequency even after the heat treatment (reflow soldering process).     

Effect of substrate temperature on structure and electrical resistivity of laser-ablated IrO2 thin films

IrO₂ thin films were prepared on Si(1 0 0) substrates by laser ablation. The effect of substrate temperature (T_sub) on the structure (crystal orientation and surface morphology) and property (electrical resistivity) of the laser-ablated IrO₂ thin films was investigated. Well crystallized and single-phase IrO₂ thin films were obtained at T_sub = 573-773 K in an oxygen partial pressure of 20 Pa. The preferred orientation of the laser-ablated IrO₂ thin films changed from (2 0 0) to (1 1 0) and (1 0 1) depending on T_sub. With the increasing of T_sub, both the surface roughness and crystallite size increased. The room-temperature electrical resistivity of IrO₂ thin films decreased with increasing T_sub, showing a low value of (42 ± 6) × 10⁻⁸ Ω m at T_sub = 773 K.     

Influence of substrate temperature and post-treatment on the properties of ZnO:Al thin films prepared by pulsed laser deposition

Highly transparent conductive Al₂O₃ doped zinc oxide (AZO) thin films have been deposited on the glass substrate by pulsed laser deposition technique. The effects of substrate temperature and post-deposition annealing treatment on structural, electrical and optical properties of AZO thin films were investigated. The experimental results show that the electrical resistivity of films deposited at 240 °C is 6.1 × 10⁻⁴ Ω cm, which can be further reduced to as low as 4.7 × 10⁻⁴ Ω cm by post-deposition annealing at 400 °C for 2 h in argon. The average transmission of AZO films in the visible range is 90%. The optical direct band gap of films was dependent on the substrate temperature and the annealing treatment in argon. The optical direct band gap value of AZO films increased with increasing annealing temperature.     

Transparent and conducting Zn-Sn-O thin films prepared by combinatorial approach

Zn-Sn-O (ZTO) films with continuous compositional gradient of Sn 16-89 at.% were prepared by co-sputtering of two targets of ZnO and SnO₂ in a combinatorial method. The resistivities of the ZTO films were severely dependent on oxygen content in sputtering gas and Zn/Sn ratio. Except for the films with Sn 16 at.%, all the as-prepared films were amorphous and maintaining the stable amorphous states up to the annealing temperature of 450 °C. Annealing at 650 °C resulted in crystallization for all the composition, in which ZnO, Zn₂SnO₄, ZnSnO₃, and SnO₂ peaks were appeared successively with increasing Sn content. Above Sn 54 at.%, the ZTO films were deduced to have a local structure mixed with ZnSnO₃ and SnO₂ phases which were more conductive and stable in thermal oxidation than ZnO and Zn₂SnO₄ phases. The lowest resistivity of 1.9 × 10⁻³ Ω cm was obtained for the films with Sn 89 at.% when annealed at 450 °C in a vacuum. The carrier concentrations of the amorphous ZTO films that contained Sn contents higher than 36 at.% and annealed at 450 °C in a vacuum were proportional to the Sn contents, while the Hall mobilities were insensitive to Sn contents and leveling in the range of 23-26 cm²/V s.     

Enhanced luminescent characteristics of laser-ablated GdVO4:Eu thin films by Li-doping

Li-doping has been used to improve luminescent characteristics of thin films. Influence of Li-doping on the crystallization, surface morphology and luminescent properties of GdVO₄:Eu³⁺ films have been investigated. Crystallinity and surface morphology of thin films have been very important factors to determine luminescent characteristics and depended on the deposition conditions. The GdVO₄:Eu³⁺ and Li-doped GdVO₄:Eu³⁺ thin films have been grown using pulsed laser deposition method on Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 600 °C under an oxygen pressure of 13.33-53.33 Pa. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. A broadband incoherent ultraviolet light source with a dominant excitation wavelength of 310 nm and a luminescence spectrometer have been used to measure photoluminescence spectra at room temperature. The emitted radiation was dominated by the red emission peak at 619 nm radiated from the transition of ⁵D₀-⁷F₂ of Eu³⁺ ions. Particularly, the peak intensity of Li-doped GdVO₄ films was increased by a factor of 1.7 in comparison with that of GdVO₄:Eu³⁺ films. The enhanced luminescence results not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. The luminescent intensity and surface roughness exhibited similar behavior as a function of oxygen pressure.     

Enhanced ferroelectric properties of vanadium doped bismuth titanate (BTV) thin films grown by pulsed laser ablation technique

Bi_3.99Ti_2.97V_0.03O₁₂ (BTV) thin films were grown by pulsed laser deposition at substrate temperatures ranging between 650 and 750 °C. The structural phase, and orientation of the deposited films were investigated in order to understand the effect of the deposition parameters on the properties of the BTV films. As the substrate temperature was increased to 700 °C, the films started showing a tendency of assuming a c-axis preferred orientation, while at lower temperatures polycrystalline films were formed. The Au/BTV/Pt capacitor showed an interesting dependence of the remnant polarization (P_r) as well as dc leakage current values on the growth temperature. The film deposited at 675 °C showed a very large 2P_r of 42 μC cm⁻², which is the largest for BTV thin films among the values reported so far.     

Structural and photoluminescence properties of SnO2:Ga films deposited on α-Al2O3 (0 0 0 1) by MOCVD

Gallium-doped tin oxide (SnO₂:Ga) films have been prepared on α-Al₂O₃ (0 0 0 1) substrates at 500 °C by the pulse mode metalorganic chemical vapor deposition (MOCVD) method. The relative amount of Ga (Ga/(Ga+Sn) atomic ratio) varied from 3% to 15%. Post-deposition annealing of the films was carried out at different temperatures for 1.5 h in ambient atmosphere . The structural, electrical, optical and photoluminescence (PL) properties of the films have been investigated as a function of annealing temperature. All the films have the rutile structure of pure SnO₂ with a strong (2 0 0) preferred orientation. A single ultraviolet (UV) PL peak near 337.83 nm was observed at room temperature for the 3% Ga-doped as-grown film and near 336 nm for the 15%-doped film, which can be ascribed to electron transition from the oxygen vacancy and interstitial Ga³⁺ donor levels to the acceptor level formed by the substitution of Ga³⁺ for the Sn site. After annealing, the luminescence spectra have changed a little bit, which is being discussed in detail.