Sn doping effects on the electro-optical properties of sol gel derived transparent ZnO films

Undoped and tin (Sn) doped ZnO films have been deposited by sol gel spin coating method. The Sn/Zn nominal volume ratio was 1, 3 and 5% in the solution. The effect of Sn incorporation on structural and electro-optical properties of ZnO films was investigated. All the films have polycrystalline structure, with a preferential growth along the ZnO (002) plane. The crystallite size was calculated using a well-known Scherrer's formula and found to be in the range of 26-16 nm. X-ray diffraction patterns of the films showed that Sn incorporation leads to substantial changes in the structural characteristics of ZnO films. The SEM measurements showed that the surface morphology of the films was affected from the Sn incorporation. The highest average optical transmittance value in the visible region was belonging to the undoped ZnO film. The optical band gap and Urbach energy values of these films were determined. The absorption edge shifted to the lower energy depending on the Sn dopant. The shift of absorption edge is associated with shrinkage effect. The electrical conductivity of the ZnO film enhanced with the Sn dopant. From the temperature dependence of conductivity measurements, the activation energy of ZnO film increased with Sn incorporation.     

Effects of atomic oxygen treatment on structures, morphologies and electrical properties of ZnO:Al films

ZnO:Al (ZAO) film has a potential application in providing spacecrafts the protection against atomic oxygen (AO) erosion. To advance the understanding of the AO resisting mechanisms and the relationships between the structures, morphologies and conductive properties of ZAO film, direct current magnetron sputtered ZAO films with different thicknesses were treated with AO in a ground-based simulation facility. The microstructure, surface chemical state, morphologies and electrical properties of pristine films and irradiated ones were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and Hall measurement. It is found that AO exposure produces novel, oriented recrystallization of the surface particles. It also increases the content of oxygen ions in fully oxidized stoichiometric surroundings on the surface, resulting in the decrease of the conductivity. As the thickness of ZAO film increases, the crystallinity, conductivity and resistance to AO erosion are all improved.     

Investigation of dielectric and electrical behavior of Mn doped YCrO3 nanoparticles synthesized by the sol gel method

In the present work Mn doped YCrO₃ nanoparticles are synthesized by the sol–gel method. Samples have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis absorption spectroscopy. The optical band gap of Mn doped YCrO₃ nanoparticles increases with increase of doping concentration. The dc resistivity of the prepared samples decreases with increasing temperature. The variation of ac conductivity with frequency has been explained by the Correlated Barrier Hoping (CBH) conduction mechanism. Dielectric permittivity of the samples was studied and it follows the power law ε^/(f)∝Tⁿ, where the temperature exponent n is found to be frequency dependent. The dielectric properties of the samples have been discussed in terms of electric modulus vector. Both activation energies due to dc resistance and dielectric response have been measured for the different samples and it is observed that it increases with the Mn content.     

Sol–gel derived zinc oxide films: Effect of deposition parameters on structure, microstructure and photoluminescence properties

ZnO films were prepared by sol–gel method and deposited onto glass substrates with spin coating system. XRD patterns and FESEM analysis were used to investigate the effect of deposition parameters such as spin speed and molar concentration on the crystallinity and surface morphology of the films. XRD patterns show that ZnO films are polycrystalline with type-wurtzite hexagonal structure. The film which is deposited at 4000 rpm and with 0.5 M sol has the best crystallinity. The FESEM micrographs showed that the surface morphology of the films was not significantly affected from the spin speed. FESEM micrographs showed that the crystallite sizes of 1000, 4000 and 5000 rpm are almost same. But 2000 and 3000 rpm have lower crystallite sizes than the others. Also, the amount of voids in the 1 M was found higher. The effect of spin speed and molar concentration on the optical properties of ZnO films was investigated by PL spectroscopy. The electrical properties of the ZnO films were investigated by using two probe methods in dark. The highest conductivity values were obtained for ZnO films prepared by 4000 spin speed and 0.5 M of concentration.     

Structural and optical properties of Mn-doped ZnO nanocrystalline thin films with the different dopant concentrations

The transparent nanocrystalline thin films of undoped zinc oxide and Mn-doped (Zn_1−xMn_xO) have been deposited on glass substrates via the sol–gel technique using zinc acetate dehydrate and manganese chloride as precursor. The as-deposited films with the different manganese compositions in the range of 2.5–20 at% were pre-heated at 100 °C for 1 h and 200 °C for 2 h, respectively, and then crystallized in air at 560 °C for 2 h. The structural properties and morphologies of the undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/Vis spectroscopy. The analyzed results indicates that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn related phases. Room temperature photoluminescence is observed for the ZnO and Mn-doped ZnO thin films.     

Effect of K-doping on structural and optical properties of ZnO thin films

In this work, K-doped ZnO thin films were prepared by a sol–gel method on Si(111) and glass substrates. The effect of different K-doping concentrations on structural and optical properties of the ZnO thin films was studied. The results showed that the 1 at.% K-doped ZnO thin film had the best crystallization quality and the strongest ultraviolet emission ability. When the concentration of K was above 1 at.%, the crystallization quality and ultraviolet emission ability dropped. For the K-doped ZnO thin films, there was not only ultraviolet emission, but also a blue emission signal in their photoluminescent spectra. The blue emission might be connected with K impurity or/and the intrinsic defects (Zn interstitial and Zn vacancy) of the ZnO thin films.     

Influence of Al concentration on electrical, structural and optical properties of Al-As codoped p-ZnO thin films

We report the influence of Al concentration on electrical, structural, optical and morphological properties of Al-As codoped p-ZnO thin films using RF magnetron sputtering. Al-As codoped p-ZnO films with different Al concentrations were fabricated using As back diffusion from the GaAs substrate and sputtering Al₂O₃ mixed ZnO targets (1, 2 and 4 at%). The grown films were investigated by Hall effect measurement, X-ray diffraction (XRD), electron probe microanalysis (EPMA), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and atomic force microscopy (AFM) to study the electrical, structural, optical and morphological properties of the films. From the XRD, it was observed that both full-width at half-maximum (FWHM) and c-axis lattice constant have similar trends with respect to Al concentration. Hall measurements showed that the hole concentration increases as the Al concentration increases from 10¹⁵ to 10²⁰ cm⁻³. The increase in hole concentration upon codoping was supported by the red shift in the near-band-edge (NBE) emission observed from room temperature PL spectra. The proposed p-type mechanism due to As_Zn-2V_Zn complex was confirmed by low temperature PL and XPS analysis. The low FWHM, resistivity and peak-to-valley roughness observed by XRD, Hall measurement and AFM, respectively, suggest that 1 at% Al-doped ZnO:As film is the best codoped film.     

Correlation between electrical and optical properties of Cr:ZnO thin films grown by pulsed laser deposition

Highly transparent and conducting Chromium doped ZnO (Cr:ZnO) thin films with preferential c-axis orientation were grown on (0 0 0 1) sapphire substrates using buffer assisted pulsed laser deposition. The resistivity of Cr:ZnO thin films was found to decrease to a minimum value of ∼1.13×10⁻³Ω cm with the increasing Cr concentration up to ∼1.9 at.% and then increase with further increase of Cr concentration. On the contrary, the band gap and carrier concentration of Cr:ZnO thin films increased up to ∼3.37 eV and ∼2×10²⁰ cm⁻³, respectively, with the increase of Cr concentration up to ∼1.9 at.%, then decreased with further increase of Cr concentration. The increase of carrier concentration and conductivity with Cr doping at low Cr concentrations (<1.9 at.%) could be attributed to the presence of Cr in +3 valence state in ZnO thus acting as donor while decrease of carrier concentration beyond ∼1.9 at.% of Cr concentration could be attributed to the charge compensating effect due to the presence of acceptor like point defects such as oxygen interstitials. This was experimentally confirmed using x-ray photoelectron spectroscopy. The observed variation in the band gap of Cr:ZnO thin films with increasing Cr doping was attributed to the competing effects of the high free carrier concentration induced Burstein-Moss blue shift and band gap narrowing.     

Effect of sol concentration on the properties of ZnO thin films prepared by sol-gel technique

ZnO thin films are deposited on the glass substrates by sol-gel drain coating technique by varying the concentration of the sol. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used to investigate the effect of sol concentration on the crystallinity and surface morphology of the films. The results show that with increase in sol concentration, the value of full width at half maximum (FWHM) of (0 0 2) peak decreases while the strain first increases and then decreases. The sol with higher concentration results in the increase in the grain size. The studies on the optical properties show that the band gap value increases from 3.27 to 3.3 eV when the sol concentration changes from 0.03 to 0.1 M. The photoconductivity studies reveal that the film for 0.05 M sol shows the maximum photoresponse for ultraviolet (UV) wavelength (<400 nm) which is co-related with the deep-level defects. The growth and decay of the photocurrent is found to be slowest for the same film.     

Annealing effects on electrical and optical properties of ZnO thin films synthesized by the electrochemical method

Microstructural and electrical properties of potentiostatically electrodeposited ZnO thin films from an aqueous bath were investigated after annealing at different temperatures in Ar and 5% H₂/Ar atmospheres. It is confirmed that the bandgap energy of ZnO thin films decreased with annealing from 3.42 to 3.27-3.29 eV by calculating the wavelength of the absorption region. The annealing at temperatures as low as 200 °C decreased the sheet resistance of ZnO thin films because of the extinction of Zn(OH)₂ in the atmosphere. In addition, the sheet resistance of ZnO thin films decreased by annealing in a 5% H₂ atmosphere, which caused an increase of carrier concentration by hydrogen reduction.     

Optical and electrical properties of aluminum-doped ZnO thin films grown by pulsed laser deposition

Transparent aluminum-doped zinc oxide (AZO) thin films were deposited on quartz glass substrates by pulsed laser deposition (PLD) from ablating Zn-Al metallic targets. The structural, electrical and optical properties of these films were characterized as a function of Al concentration (0-8 wt.%) in the target. Films were deposited at a low substrate temperature of 150 °C under 11 Pa of oxygen pressure. It was observed that 2 wt.% of Al in the target (or 1.37 wt.% of Al doped in the AZO film) is the optimum concentration to achieve the minimum film resistivity and strong ultraviolet emission. The presence of Al in the ZnO film changes the carrier concentration and the intrinsic defects.     

Effects of annealing on structural,optical and electrical properties of Al-doped ZnO thin films

Transparent conducting oxide (TCO) thin films such as SnO2, In2O3, and Cd2SnO4, have been used extensively as sensor devices, surface acoustic wave devices, coating to heat glass windows and transparent electrodes for solid state display devices, solar cells[1,2] because of their high optical transparency in the visible range, infrared reflec-tance and low d.c. resistivity. Although SnO2 film was developed early, nowadays Sn-doped In2O3 (ITO) films are the predominant TCO thin film in …     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

Study on the ferromagnetism in Co and N doped ZnO thin films

Present investigation reports the structural, optical and magnetic properties of co-doping of Co and N ions in ZnO samples, prepared by two distinct methods. In the first method, samples are synthesized by Sol–gel technique in which the Co and N are co-doped simultaneously during the growth process itself. In the second case, N ions are implanted in the Co doped ZnO thin films grown by Pulsed Laser Deposition (PLD). Structural studies showed that the nitrogen implantation on Co doped ZnO samples developed compressive stress in the films. X-ray photoelectron spectroscopy confirmed the doping of Co and N in ZnO matrix. In the Resonant Raman scattering multiple LO phonons up to fifth order are observed in the (Co, N) co-doped ZnO. Photoluminescence spectra showed that there is reduction in the bandgap due to the presence of Co in the lattice and also the presence of Zn vacancies in the films. All samples showed ferromagnetic behavior at room temperature. The magnetic moment observed in the implanted films is found to be varied with the different dosages of the implanted N ions. First principle calculations have been carried out to study the possible magnetic interaction in the co-doped system. Present study shows that the ferromagnetic interaction is due to the hybridization between N 2p and Co 3d states in the (Co, N) co-doped ZnO and is very sensitive to the geometrical configurations of dopants and the vacancy in the ZnO host lattice.     

Correlation between electrical, optical properties and Ag centers of ZnO:Ag thin films

ZnO:Ag films have been fabricated on a n-Si (1 1 1) substrate and then annealed in situ in an O₂ ambient, using Ag₂O as a silver dopant by pulsed laser deposition. Hall measurements reveal that the films prepared at 400 and 450 °C show p-type behavior with a hole concentration of 6.3×10¹⁶–1.2×10¹⁷ cm^–3 and a mobility of 2.48–3.30 cm²/V s. By combining Hall measurements, electron paramagnetic resonance (EPR) signals, and photoluminescence (PL) spectra, a correlation is observed between the free hole carriers, the Ag²⁺ centers, and the neutral acceptor bound excitons. Additionally, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I–V characteristic.     

Effects of post-annealing on structural, optical and electrical properties of Al-doped ZnO thin films

Aluminum-doped zinc oxide (AZO) films were deposited at 400 °C by radio-frequency magnetron sputtering using a compound AZO target. The effects of annealing atmospheres as well as hydrogen annealing temperatures on the structural, optical and electrical properties of the AZO films were investigated. It was found that the electrical resistivity varied depending on the atmospheres while annealing in air, nitrogen and hydrogen at 300 °C, respectively. Comparing with that for the un-annealed films, the resistivity of the films annealed in hydrogen decreased from 9.8 × 10⁻⁴ Ω cm to 3.5 × 10⁻⁴ Ω cm, while that of the films annealed in air and nitrogen increased. The variations in electrical properties are ascribed to both the changes in the concentration of oxygen vacancies and adsorbed oxygen at the grain boundaries. These results were clarified by the comparatively XPS analyzing about the states of oxygen on the surface of the AZO films. There was great increase in electrical resistivity due to the damage of the surfaces, when AZO films were annealed in hydrogen with a temperature higher than 500 °C, but high average optical transmittance of 80-90% in the range of 390-1100 nm were still obtained.     

Effects of deposition temperatures and annealing conditions on the microstructural, electrical and optical properties of polycrystalline Al-doped ZnO thin films

Al-doped ZnO (AZO, ZnO:Al₂O₃ = 98:2 wt%) films are deposited on different substrates by an RF magnetron sputtering and subsequently annealed at three different conditions to investigate the microstructural, electrical, and optical properties. X-ray diffraction and scanning electron microscope results show that all the samples are polycrystalline and the samples rapid-thermal-annealed at 900 °C in an N₂ ambient contain larger grains compared to the furnace-annealed samples. It is shown that the sample deposited at room temperature on the sapphire gives a resistivity of 5.57 × 10⁻⁴ Ω cm when furnace-annealed at 500 °C in a mixture of N₂:H₂ (9:1). It is also shown that the Hall mobility vs. carrier concentration (μ-n) relation is divided into two groups, depending on the annealing conditions, namely, either rapid-thermal annealing or furnace annealing. The relations are described in terms of either grain boundary scattering or ionized impurity scattering mechanism. In addition, the samples produce fairly high transmittance of 91-96.99% across the wavelength region of 400-1100 nm. The optical bandgaps of the samples increase with increasing carrier concentration.     

Effect of annealing on the optical and electrical properties of ZnO:Er films

The effect of dopant concentration and annealing in the oxidizing atmosphere on the structural, optical, and electrical properties of ZnO:Er films deposited on sapphire substrates by the electron-beam evaporation method is investigated. The optical and electrical properties of these films were studied by UV-VIS-IR absorption and reflection spectroscopy, photoluminescence, and resistivity measurements. Experimental results reveal that as-deposited ZnO:Er films have both high transmittance in the visible range and low electrical resistivity and can be used as efficient transparent conducting oxides (TCOs). These films annealed in the oxidizing atmosphere have a visible emission band which can be used to fabricate light-emitting diodes.     

Thermal conductivity of nanoscale polycrystalline ZnO thin films

Thermal conductivities (TCs) of ZnO thin films of thickness 80-276 nm prepared by sol-gel method are measured by the transient thermoreflectance (TTR) system. The obtained TCs ranging from 1.4 to 6.5 W/m K decrease while the thickness decrease. The measured TCs are much smaller than those of bulk ZnO, which is about 100 W/m K. The possible reasons for the decrease are the grain boundary and defects. The latter is the dominating one from the analysis.