GZO Films Research Articles

Structural, optical and electrical properties of sol–gel prepared Ga:ZnO thin film

Transparent conductive gallium-doped zinc oxide films (GZO) with different thickness were grown on a glass substrate by cost effective sol–gel spin coating technique using zinc acetate and gallium nitrate as precursors for Zn and Ga ions, respectively. The structural, optical and electrical properties of the films were analysed as a function of film thickness using X-ray diffraction (XRD), spectrophotometry and Hall effect measurements. X-ray diffraction analysis showed the polycrystalline nature of the films with a hexagonal (wurtzite) crystal structure and a preferred orientation with c-axis, perpendicular to the substrate. Experimental results revealed that within a certain range of thickness, the grain size along with the root mean square (RMS) surface roughness increase with film thickness. The strain relaxation was found to be maximum for the thicker film. The average optical transmittance of all the films was over 86% and a sharp fundamental absorption edge with a slight red shifting was observed in the visible region. A lowest resistivity 3.66 × 10(3 Ω cm and highest carrier concentration were achieved for GZO film of thickness 396 nm. The result obtained from this study showed that the structural, optical and electrical properties of GZO films deposited by sol–gel method were strongly affected by the film thickness.

Investigation on the Effect of the Substrate Temperature on the Photoelectric Properties of the Ga Doped ZnO Film

The Ga doped ZnO film (GZO) was fabricated via magnetron sputtering on the substrate of silica glass. The effect of substrate temperature on the photoelectric properties of GZO film, such as morphology, grain size, crystal structure and transparency was studied. The results showed us that the crystallinity of GZO film was improved by increasing the substrate temperature . The GZO film exhibited high transmittance (above 80% in the visible region) at the substrate temperature higher than 200°C. The lowest resistivity of 4.45×10-4Ω·cm and highest hall mobility of 11.7 cm2 v-1s-1 were obtained when the substrate temperature was 300°C.

Sol ageing effect on the structural, optical and electrical properties of Ga-doped ZnO thin films

Gallium-doped zinc oxide thin films (GZO) were grown on a glass substrate by a simple sol–gel process and spin coating technique. The effects of sol ageing time on the structural, optical and electrical properties of the GZO films were investigated. Experimental results showed that the microstructure, optical transmittance and electrical resistivity of the GZO films depend directly on the sol ageing time. XRD studies revealed the polycrystalline nature of the films with the c-axis grain orientation. Optical transmittance of the films was higher than about 82% within the visible region and the optical direct band gap was increased with increasing sol ageing time. A minimum resistivity of 3.16 × 10−5 Ω m was observed in the film deposited by a sol aged for 48 h. These results indicate that an appropriate ageing time of the sol is important for the improvement of the properties of GZO films derived from sol–gel method.

Enhanced Light Scattering by Preferred Orientation Control of Ga Doped ZnO Films Prepared through MOCVD

We have explored the effective approach to fabricate GZO/ZnO films that can make the pyramidal surface structures of GZO films for effective light scattering by employing a low temperature ZnO buffer layer prior to high temperature GZO film growth. The GZO thin films exhibit the typical preferred growth orientations along the (002) crystallographic direction at deposition temperature of 400°C and SEM showed that column-like granule structure with planar surface was formed. In contrast, GZO films with a pyramidal texture surface were successfully developed by the control of (110) preferred orientation. We found that the light diffuse transmittance of the film with a GZO (800 nm)/ZnO (766 nm) exhibited 13% increase at 420 nm wavelength due to the formed large grain size of the pyramidal texture surface. Thus, the obtained GZO films deposited over ZnO buffer layer have high potential for use as front TCO layers in Si-based thin film solar cells. These results could develop the potential way to fabricate TCO based ZnO thin film using MOCVD or sputtering techniques by depositing a low temperature ZnO layer to serve as a template for high temperature GZO film growth. The GZO films exhibited satisfactory optoelectric properties.

Influence of a Ni interlayer on the optical and electrical properties of trilayer GZO/Ni/GZO films

Trilayer GZO/Ni/GZO films were deposited onto polycarbonate (PC) substrates with RF and DC magnetron sputtering, and then the influence of a Ni interlayer on the optical and electrical properties of the films was investigated. A 2-nm-thick Ni interlayer decreased the resistivity to 6.4×10−4Ωcm and influenced the optical transmittance.Although optical transmittance deteriorated with Ni insertion, the films showed a relatively high optical transmittance of 74.5% in the visible wavelength region. The figure of merit (FOM) of a GZO single layer film was 1.2×10−4Ω−1, while that of the GZO/Ni/GZO films reached a maximum of 8.2×10−4Ω−1.Since a higher FOM results in higher quality transparent-conductive oxide (TCO) films, it is concluded that GZO films with a 2nm Ni interlayer have better optoelectrical performance than single-layer GZO films.

Effect of an Ag Insertion Layer on the Optical and Electrical Properties of Ga Doped Zinc Oxide Films.

GZO/Ag/GZO films were investigated for use as high quality transparent conductive electrodes. The GZO and Ag films were deposited by RF sputtering and electron beam evaporation, respectively, at room temperature. The effects of Ag thickness and post heat treatment on the structural, electrical and optical properties of these multilayer films were investigated. The insertion of the Ag layer with optimized thickness between the GZO layers and the optimized annealing temperature improved the electrical and optical properties of the GZO/Ag/GZO film due to the very low resistivity and surface plasmon effect of the Ag layer. The best multilayer film exhibited a low resistivity of 2.2 x 10(-5) Ω · cm and a transmittance of 88.9%.

Influence of sputtering power on the properties of thin layers of GZO for photovoltaic applications

In the present work, we have deposited gallium doped zinc oxide thin films by magnetron sputtering technique based nanocrystalline particles elaborated by sol–gel method. In the first step, the nanoparticles were synthesized by sol–gel method using supercritical drying in ethyl alcohol. The structural studied by X-ray diffractometry indicates that GZO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy measurements have shown that very small particles of GZO are present in the aerogel powder. Then, thin films were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature. The influence of RF sputtering power on structural, morphological, electrical, and optical properties were investigated. It has been found that all of the films deposited were polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The film deposited at 60 W showed the lowest electrical resistivity of 3.5 × 10−3 Ω cm achieved through the highest Hall mobility of 9.30 cm2 V−1 s−1. All the GZO films in this study showed the optical transmittances higher than 80 %.

Zn-aided defect control for ultrathin GZO films with high carrier concentration aiming at alternative plasmonic metamaterials

In this work, (0–10 nm) Zn/100 nm ZnO:Ga ultrathin films are deposited on glass substrate at room temperature by magnetron sputtering, with a post-rapid thermal annealing (RTA) at 500 °C for 1 min, which causes a dramatic improvement in carrier concentration due to elimination of Zn-vacancy defects. Depositing different Zn thickness, only 8 nm Zn/100 nm GZO thin film exhibits the highest carrier concentration of 1.02 × 1021 cm−3 and the lowest resistivity of 4.0 × 10−4 Ω cm. Higher electronic concentration shifts the zero-crossover of the real permittivity below 1.3 μm, which confirms the metal-like optical properties in the near-infrared (NIR) range. Optical losses in these annealed Zn/GZO films are four times smaller than conventional Ag films in the NIR. The average transmittances of all the annealed GZO thin films were above 84% in the visible range. The GZO ultrathin film deposited by this method is a promising low-loss alternative material to conventional metals for plasmonic devices operating in the NIR.

Preparation of Transparent Metal Films, Gallium-Doped Zinc-Oxide (Ga2O3)x (ZnO)100-x Films by Using Facing Target Sputtering System

(Ga2O3)x(ZnO)100-x, x = 3, 5, 7, 9 wt.%, (GZO) films were prepared at room temperature by using a conventional rf-magnetron sputtering method. Their electrical resistivity was investigated as a function of the Ga2O3 content. The GZO film with x = 7 wt.%, shows the lowest resistivity of 1.5×10−3Ω. cm. This GZO films were also prepared at various substrate temperatures from room temperature to 400°C, Their electrical resistivity was found to be improved as the substrate temperature was increased, A very low resistivity of 4.5×10−4Ω.cm was obtained in the film prepared at the substrate temperature of 300°C. In addition, we found that the GZO films prepared by using facing target sputtering (FTS) system showed a dramatically improved conductivity as compared with that of the film prepared by the conventional sputtering system. In particular, we also found that the lowest resistivity of 2.8×10−4Ω.cm that is almost comparable with that of ITO film was obtained in the GZO films prepared at the substrate temperature of 300°C by using the facing target sputtering (FTS) system.

Comparative study of thermal stability of aluminium- and gallium-doped ZnO thin films prepared by sol–gel method

To study the thermal stability of Al- and Ga-doped ZnO (AZO and GZO) films, these films with a doping concentration from 0·5 to 3 at-% have been prepared by sol–gel method on glass substrate followed by annealing in air. It has been found out that the AZO and GZO films have similar thermal stability, and Ga dopant cannot improve the stability. Moreover, the doping concentration has no prominent effect on the thermal stability. The resistivity of the films is stable when the annealing temperature is lower than 250°C and increases rapidly after that, while the transmittance increases with annealing temperature. The variations of the resistivity and the transmittance are closely related to the microstructure, and vacancy and electron concentration affected by the annealing treatment.

THERMOELECTRIC AND MAGNETO-THERMOELECTRIC PROPERTIES OF Ga-DOPED ZnO THIN FILMS BY RF MAGNETRON SPUTTERING

Zn (1-x) Ga x O thin films (x = 0.01, 0.03, 0.05, 0.07 named as GZO1, GZO2, GZO3, GZO4, respectively) were deposited on glass substrates by RF magnetron sputtering. The crystal structure, electrical, thermoelectric and magneto-thermoelectric properties of GZO films were investigated. It is found that all the GZO films are polycrystalline and preferentially oriented in the c-axis. The electrical resistivity of GZO films decreased first with increasing Ga doping content before it reached a minimum at x = 0.05, and then increased with further increasing Ga doping content. The magnetic fields (B) ranging from 0 to 1.5 T are perpendicularly applied to the films to study the magneto-thermoelectric properties. It is observed that the absolute values of Seebeck coefficients (|S|) of GZO1, GZO2, GZO3 show marked variation with magnetic field and obtain the maximum value at B = 0.5 T. Whereas the |S| value of GZO4 fluctuates slightly with magnetic field and reaches its peak at B = 1.0 T. The magneto-thermoelectric properties are analyzed and we propose that this behavior is mainly attributed to the effect of magnetic field on the electron transport.

The Microstructure of Aging ZnO, AZO, and GZO Films

The Microstructure of Aging ZnO, AZO, and GZO Films

The Microstructure of Aging ZnO, AZO, and GZO Films

The Microstructure of Aging ZnO, AZO, and GZO Films

Transparent conductive Al and Ga doped ZnO films deposited using off-axis sputtering

Al and Ga doped ZnO (AZO and GZO) films were deposited using an off-axis dc magnetron sputtering method. At the off-axis positions, both the mobility and carrier density increased, resulting in enhanced conductivity of both the AZO and GZO films due to an increase in the crystallinity. The lowest resistivities of the AZO and GZO films deposited at room temperature were 1.1×10−3Ωcm and 6.5×10−4Ωcm, respectively. Increasing the substrate temperature up to 130°C led to a decrease in the lowest resistivity to 6.1×10−4Ωcm for the AZO films. The transmittance of all films was above 80% in the visible region. These results suggest that off-axis magnetron sputtering might be a potentially effective deposition method with the reduced bombardments from high-energy particles.

Influences of deposition power of GZO thin films on the properties of the heterojunction diode based on a NiO/GZO bi-layer structure

A compound of ZnO with 3 wt% Ga 2 O 3 (ZnO : Ga 2 O 3 = 97 : 3 in wt%, GZO) was sintered at 1400oC as a GZO target. Radio frequency magnetron sputtering was used to deposit nickel oxide thin films (NiO, deposition power of 100 W) and GZO thin films (deposited at 300°C by changing the deposition power from 50 W to 150 W) on glass substrates to form p(NiO)-n(GZO) heterojunction diodes with high transmittance. The structural, optical, and resistivity properties of the GZO and NiO thin films and NiO/GZO heterojunction devices were investigated with scanning electron microscopy (SEM), X-ray diffraction (XRD) patterns, UV-visible spectroscopy, Hall-effect analysis, and current–voltage ( I – V ) analysis. XRD analysis showed that only the (111) diffraction peak of NiO and the (002) and (004) diffraction peaks of ZnO (GZO) were observable in the NiO/GZO heterojunction devices, and the GZO thin films showed a good c-axis orientation perpendicular to the glass substrates. The variations in the optical band gap ( E g value) of the GZO thin films were evaluated from the plots of ( αhv ) = c ( hν – E g ) 1/2 , revealing that the measured E g value decreased with increasing deposition power. For the deposited GZO thin films, both the carrier concentration and mobility linearly decreased and the resistivity increased approximately with increasing deposition power. When the sputtering deposition power for the GZO thin films was deposited at different power, the I – V characteristics confirmed that a p-n junction characteristic was successfully formed in the NiO/GZO heterojunction devices.

Effect of growth temperature on structural, electrical, and optical properties of Gd‐doped zinc oxide films

AbstractGd‐doped ZnO (GZO) films were deposited on glass substrates at various growth temperatures by using radio‐frequency (rf) magnetron sputtering. The experimental data showed that the growth temperature had a significant effect on the structural, optical, and electrical properties of the GZO films. The GZO film deposited at 400 °C exhibited a preferential growth orientation along the (002) plane with a thickness of 1480 nm, an average optical transmittance of 86.5% in the visible wavelength range, an optical band gap of 3.18 eV, and an electron concentration of 1.9 × 1020 cm−3, where the highest figure of merit was obtained. The increase in the figure of merit results from the decrease in the electrical resistivity with increasing growth temperature. The optical band gap energy Eg as a function of the growth temperature T, calculated by using the Tauc model and parabolic bands, is expressed as eV. The results suggest that the optimum growth temperature for depositing high‐quality GZO films is 400 °C.

Transparent Conductive Oxide GZO Thin Films by Sol-Gel Process

In this work, GZO thin films were prepared by sol-gel process and spin coating technique. The XRD results showed the preferential c-axis orientation of the crystallites and the presence of the wurite phase of ZnO and it were suggested that the presence of Ga might be changed the d-spacing of ZnO to formation the Ga-doped zinc oxide. The effects of Ga amount on the conductivity and transparency were studied. The electrical resistivity for the GZO film doped 2 at% of Ga could be lowered to be 7.510-3Ω-cm with the calcination temperature was 550°C and hydrogen treatment was conducted in the Ar/H2 (97/3) atmosphere at 500°C. In addition, the optical transmittances of GZO thin films were higher than 90% in visible wavelength region.

Enhancement of the light-scattering ability of Ga-doped ZnO thin films using SiOx nano-films prepared by atmospheric pressure plasma deposition system

To enhance the light-trapping qualities of silicon thin-film solar cells, the use of transparent conductive oxide with high haze and high conductivity is essential. This study investigated an eco-friendly technique that used bilayer Ga-doped zinc oxide/SiOx films prepared with an atmospheric pressure plasma jet to achieve high haze and low resistivity. A minimum resistivity of 6.00×10−4Ω·cm was achieved at 8at.% gallium doping. Examination of X-ray diffraction spectra showed that increased film thickness led to increased carrier concentration in GZO bilayers. The optimal bilayer GZO film achieved considerably higher haze values in the visible and NIR regions, compared with Asahi U-type fluorine doped tin oxide.

Effect of ZnO Buffer Layer on the Bending Durability of ZnO:Ga Films Grown on Flexible Substrates: Investigation of Surface Energy, Electrical, Optical, and Structural Properties

ZnO:Ga (GZO) transparent conducting oxide (TCO) films are deposited on flexible polyethersulfone (PES) substrates using the radio frequency sputtering technique. The bending durability of flexible TCOs is improved by inserting 100-nm-thick ZnO buffer layers. The strain of the samples with and without buffer layers arising from bending is studied using X-ray diffraction. After the insertion of 100-nm-thick ZnO buffer layers, the strain of GZO films without ZnO after outward and inward bending for 2000 cycles decreases from 2.063 ×10-3 and 2.203 × 10-3 to 1.74 × 10-3 and 1.966 × 10-3, respectively. Such strain variation is caused by the difference in adhesive force at the surface of 100-nm-thick ZnO/PES and PES. The surface energy of PES and 100-nm-thick ZnO/PES bent outwards and inwards for 2000 cycles increased from 34.38 and 30.56 to 36.45 and 36.03 mJ/m2, respectively.

Temperature-dependent electrical property and optical transparency of Al/Ga-doped ZnO double-layer system

Al (5 nm)/Ga-doped ZnO (GZO, 100 nm) double-layer films were prepared at room temperature by magnetron sputtering. It is found that the crystal structure of GZO is degraded due to the existence of Al layer. Semiconductor transport behavior is observed in GZO and Al/GZO films in the temperature range of 80∼360 K. As opposed to that of GZO, the resistivity of Al/GZO shows a significant decrease with increasing the temperature from 320 to 360 K. To understand the temperature dependent resistivity, Al (5 nm)/GZO film was annealed in vacuum in the temperature range of 398∼573 K. High-resolution TEM observations reveal that Al grains become more and more isolated as the annealing temperature increases. The decreasing resistivity above 320 K for the Al/GZO system is considered to be caused by the substitution of Al atoms for Zn atoms at the interface, showing an improvement in the transmittance with over 90 % especially at 398 K.