GZO Thin Films Research Articles

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.

The optical and electrical properties of gallium-doped ZnO thin film with post-annealing processes of various atmospheres

In this study, the GZO thin film were deposited with different RF powers and plasma gas of pure argon, 5% oxygen to argon ratio, and 10% oxygen argon ratio. After that, post-thermal annealing processes were performed at the temperature of 300°C to 500°C under vacuum, nitrogen, or acetylene ambient. The carrier concentrations and mobility exhibited different dependencies on these fabrication parameters, and that would reverse the conductivity order of as-sputtered samples. As a result, the carbon atom in the acetylene dissolved into the GZO thin film during post-thermal annealing and benefited the free carrier concentrations as another effective donor besides the gallium. The optical bandgap increased due to the increasing free carrier concentration, and made transparency still above 80%.

The Influence of Electric Parameters on Film Quality of GZO Thin Film Fabricated by APPJ Process

In this paper, APPJ (Atmospheric pressure Pules arc Plasma Jet) is used to generate a DC pulse source depositing GZO thin film under atmospheric pressure. Thus, no vacuum chamber needed leads to the cost downward. With scanning operation, makes single unit area into large size area. Several key process parameters have been studied, including the power supply voltage, DC pulse, the length of the nozzle extended head, and depositing gap to understand their relationship with the film quality and atmospheric plasma state.In this study, with adjusting DC pulse, the pulse frequency is found to have a great impact on the plasma state and the film quality. When the pulse frequency is near 25 kHz, lower sheet resistance can be retained. Besides, adjusting Toff time, the plasma and thin film quality are influenced more than Ton time. By changing the power supply voltage, the secondary-side voltage decreases with increasing of the instantaneous current; moreover, the plasma will become more intense.

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.

Effect of a ZnO buffer layer on the properties of epitaxial ZnO:Ga films deposited on c-sapphire substrate

Bi-layer ZnO films with 2wt.% Al (AZO; ZnO:Al) and 4wt.% Ga-doped (GZO; ZnO:Ga) were deposited on the non-buffered and buffered c(0001)-sapphire(Al2O3) substrates respectively by Pulsed Laser Deposition (PLD). The effect of a ZnO buffer layer on the crystallinity and electrical properties of the GZO thin films was investigated. X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) studies showed that the GZO thin film on a buffered substrate was epitaxially grown with an orientation relationship of (0001) [112¯0]GZO||(0001)[112¯0]Al2O3. However, GZO thin film on a non-buffered substrate was grown as a monocrystalline hexagonal wurtzite phase with c-axis preferred, out-of-plane orientation, and random in-plane orientation. The electrical resistivity of the GZO thin films was improved by introducing a ZnO buffer layer from 2.2×10-4Ωcm to 1.2×10-4Ωcm, respectively. In a word, it was found in the films that more preferred c-axis orientation texture and reduction of the defects such as stacking faults and dislocations, with introducing a ZnO buffer layer.It was seen that the ZnO buffer layer had a great influence on the orientation and defect density of GZO thin films from X-ray Diffraction (XRD) peaks and High Resolution Transmission Electron Microscopy (HRTEM) images.

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.

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.

Thermal Stability of Gallium-Doped Zinc Oxide Thin Film on Glass Substrates by an RF Sputtering Process

The effects of a heat treatment on the structural and electrical properties of GZO thin films grown by RF magnetron sputtering were investigated. The heat treatment involved temperatures in the range from 200 degrees C to 500 degrees C under air. As the temperature was increased, the electrical properties of GZO thin films increased exponentially and the surface morphology was drastically altered. The effect of temperature is discussed based on electrical and structural characterization of the materials.

Using SiOx nano-films to enhance GZO Thin films properties as front electrodes of a-Si solar cells

One of the essential applications of transparent conductive oxides is as front electrodes for superstrate silicon thin-film solar cells. Textured TCO thin films can improve absorption of sunlight for an a-Si:H absorber during a single optical path. In this study, high-haze and low-resistivity bilayer GZO/SiOx thin films prepared using an atmospheric pressure plasma jet (APPJ) deposition technique and dc magnetron sputtering. The silicon subdioxide nano-film plays an important role in controlling the haze value of subsequent deposited GZO thin films. The bilayer GZO/SiOx (90sccm) sample has the highest haze value (22.30%), the lowest resistivity (8.98×10−4Ωcm), and reaches a maximum cell efficiency of 6.85% (enhanced by approximately 19% compared to a sample of non-textured GZO).

The Effect of Annealing Temperature on the Opt-Electric Properties of Ti:GZO Transparent Conducting OxidesThin Film

This study utilizes radio frequency magnetron sputtering(RF-sputtering) to deposit GZO transparent conductive film and Ti thin film on the same corning glass substrate, then treats GZO/Ti thin film with rapid thermal annealing. The annealing temperature is 300, 500 and 550°C, respectively. Moreover, the effects of process parameters on resistivity and optical properties are investigated. The deposited rate, microstructure, thickness and Optical transmission of Ti:GZO thin film are performed. For example, the thicknesses of films were determined by -step profilometer. The crystalline characteristics of thin films were investigated by X-ray diffraction (XRD). Ga and Ti concentration in ZnO film were determined by energy dispersive X-ray spectroscopy (EDS). The electrical properties of the Ti:GZO thin films were measured by Four point probe. The optical properties of Ti:GZO thin films were examined using UV–vis spectrophotometer. The results show that the transmittance of Ti:GZO thin film exhibited an excellent transparency in the visible light field. The resistivity of Ti:GZO decrease with increasing annealing temperature.

Optical and Electrical Properties of the Different Magnetron Sputter Power 300°C Deposited -ZnO Thin Films and Applications in p-i-n -Si:H Thin-Film Solar Cells

A compound of ZnO with 3 wt% Ga2O3(ZnO : Ga2O3 = 97 : 3 in wt%, GZO) was sintered at C as a target. The GZO thin films were deposited on glass using a radio frequency magnetron sputtering system at C by changing the deposition power from 50 W to 150 W. The effects of deposition power on the crystallization size, lattice constant (c), resistivity, carrier concentration, carrier mobility, and optical transmission rate of the GZO thin films were studied. The blue shift in the transmission spectrum of the GZO thin films was found to change with the variations of the carrier concentration because of the Burstein-Moss shifting effect. The variations in the optical band gap () value of the GZO thin films were evaluated from the plots of , revealing that the measured value decreased with increasing deposition power. As compared with the results deposited at room temperature by Gong et al., (2010) the C deposited GZO thin films had apparent blue shift in the transmission spectrum and larger value. For the deposited GZO thin films, both the carrier concentration and mobility linearly decreased and the resistivity linearly increased with increasing deposition power. The prepared GZO thin films were also used as transparent electrodes to fabricate the amorphous silicon thin-film solar cells, and their properties were also measured.

Using Flexible Polyimide as a Substrate to Deposit ZnO:Ga Thin Films and Fabricate p-i-n -Si:H Thin-Film Solar Cells

The GZO thin films were deposited on the polyimide (PI) substrates to investigate their properties for the possibly flexible applications. The effects of substrate temperature (from room temperature to 200°C) on the surface and cross-session morphologies, X-ray diffraction pattern, optical transmission spectrum, carrier concentration, carrier mobility, and resistivity of the GZO thin films on PI substrates were studied. The measured results showed that the substrate temperature had large effect on the characteristics of the GZO thin films. The cross-section observations really indicated that the GZO thin films deposited at 200°C and below had different crystalline structures. The value variations in the films’ optical band gap () of the GZO thin films were evaluated from plots of, revealing that the measured values increased with increasing deposition temperature. Finally, the prepared GZO thin films were also used as the transparent electrodes to fabricate the -Si amorphous silicon thin-film solar cells on the flexible PI substrates, and the properties of which were also measured. We would also prove that substrate temperature of the GZO thin films had large effect on the characteristics of the fabricated -Si amorphous silicon thin-film solar cells.

Influence of Annealing Temperature on the Characteristics of Ti‐Codoped GZO Thin Solid Film

This study utilizes radio frequency magnetron sputtering (RF sputtering) to deposit GZO transparent conductive film and Ti thin film on the same corning glass substrate and then treats GZO/Ti thin film with rapid thermal annealing. The annealing temperatures are 300°C , 500°C, and 550°C, respectively. Ti:GZO transparent conductive oxide (TCO) thin films are deposited on glass substrates using a radio frequency magnetron sputtering technique. The thin films are then annealed at temperatures of 300°C, 500°C, and 550°C, respectively, for rapid thermal annealing. The effects of the annealing temperature on the optical properties, resistivity, and nanomechanical properties of the Ti:GZO thin films are then systematically explored. The results show that all of the annealed films have excellent transparency (~90%) in the visible light range. Moreover, the resistivity of the Ti:GZO films reduces with an increasing annealing temperature, while the carrier concentration and Hall mobility both increase. Finally, the hardness and Young’s modulus of the Ti:GZO thin films are both found to increase as the annealing temperature is increased.

Influence of Annealing Time on the Properties of GZO Thin Films Fabricated by Direct Current Magnetron Sputtered

The films were deposited on glass slide substrates by DC magnetron sputtering method by using a ZnO target doped with Ga2O3 of 3wt%, then annealing processing were implemented respectively under the temperature of 250 °C with the time of 0,30,60,90 and 120 minutes.Effects of sputtering on the structural and optical and electrical properties of GZO films had been investigated. The results showed that GZO films with high quality could be fabricated after vacuum-annealed. crystal face of GZO films had a good tendency of c axis. the (002) diffraction peak reached a maximum at the annealing time of 1.5 hours; at the same time ,crystal grain became larger and crystal boundaries narrow, film’s resident stress reduced to 0.5 Mpa.With the annealing time increasing, the resistivity of GZO films decreased and reached the minimum which was 9.1×10-4 Ω·cm at 1.5 hours. While the average transmittance decreased sharply after the time of 1.5 hours in visible region. Consequently, the best annealing time is 1.5 hours.

Comparative studies of Al-doped ZnO and Ga-doped ZnO transparent conducting oxide thin films

We have investigated the influences of aluminum and gallium dopants (0 to 2.0 mol%) on zinc oxide (ZnO) thin films regarding crystallization and electrical and optical properties for application in transparent conducting oxide devices. Al- and Ga-doped ZnO thin films were deposited on glass substrates (corning 1737) by sol–gel spin-coating process. As a starting material, AlCl3⋅6H2O, Ga(NO3)2, and Zn(CH3COO)2⋅2H2O were used. A lowest sheet resistance of 3.3 × 103 Ω/□ was obtained for the GZO thin film doped with 1.5 mol% of Ga after post-annealing at 650°C for 60 min in air. All the films showed more than 85% transparency in the visible region. We have studied the structural and microstructural properties as a function of Al and Ga concentrations through X-ray diffraction and scanning electron microscopy analysis. In addition, the optical bandgap and photoluminescence were estimated.

Influence of the kind and content of doped impurities on impurity-doped ZnO transparent electrode applications in thin-film solar cells

The influence of the kind and content of doped impurity on the electrical properties and their stability as well as on the light scattering characteristics and the surface texture formation obtainable by wet-chemical etching was investigated to develop transparent conducting impurity-doped ZnO thin films suitable for transparent electrode applications in thin-film solar cells. Al-, B- and Ga-doped ZnO (AZO, BZO and GZO) thin films were prepared on glass substrates at 200°C by doping each impurity at an appropriate content to achieve lower resistivity using a pulsed laser deposition and by varying the doped Al or Ga impurity content using r.f. superimposed d.c. magnetron sputtering deposition. The difference in the resulting electrical properties and their stability (air at 85% relative humidity and 85°C) among the AZO, BZO and GZO thin films is attributed to the content of each impurity rather than the kind of impurity. In evaluations of the light scattering characteristics and the surface texture formation in a 0.1% HCl solution at 25°C, the difference in the haze value obtainable among the AZO, BZO and GZO thin films is mainly attributed to the content of each impurity doped into the films. The AZO, BZO and GZO films prepared with doped impurity contents below approximately 2at.% are suitable for transparent electrode applications in thin-film solar cells, irrespective of the kind of impurity as well as the deposition method used.

Impurity-doped ZnO Thin Films Prepared by Physical Deposition Methods Appropriate for Transparent Electrode Applications in Thin-film Solar Cells

This paper describes the development of transparent conducting impurity-doped ZnO thin films that would be appropriate for applications as transparent electrodes in thin-film solar cells. Transparent conducting Al-, B- and Ga-doped ZnO (AZO, BZO and GZO) thin films were prepared in a thickness range from 500 to 2000 nm on glass substrates at 200°C using various physical deposition methods: BZO films with vacuum arc plasma evaporation, AZO and GZO films with different types of magnetron sputtering depositions (MSDs) and all films with pulsed laser deposition (PLD). The suitability and stability of the electrical properties and, in addition, the suitability of the light scattering characteristics and surface texture formation were investigated in the prepared thin films. In particular, the suitability and stability evaluation was focused on the use of AZO, BZO and GZO thin films prepared by doping each impurity at an appropriate content to attain the lowest resistivity. The higher Hall mobility obtained in impurity-doped ZnO thin films with a resistivity on the order of 10−4 Ωcm was related more to the content, i.e., the obtained carrier concentration, rather than the kind of impurity doped into the films. The stability of resistivity of the BZO thin films in long-term moisture-resistance tests (in air at 85% relative humidity and 85°C) was found to be lower than that of the AZO and GZO thin films. The surface texture formation was carried out by wet-chemical etching (in a 0.1% HCl solution at 25°C) conducted either before or after being heat-treated either with rapid thermal annealing (RTA) or without RTA. The suitability of the light scattering characteristics and the surface texture formation obtainable by wet-chemical etching (for use in transparent electrode applications) was considerably dependent on the deposition method used as well as whether the wet-chemical etching was conducted with or without RTA. A significant improvement of both transmittance and haze value at wavelengths up to about 1200 nm in the near-infrared region was attained in surface-textured AZO films that were prepared by r.f. power superimposed d.c. MSD as well as etched after being heat treated with RTA at 500°C for 5 min in air. The obtained suitability and stability in impurity-doped ZnO thin films were related more to the content rather than the kind of impurity doped into the films as well as to the deposition method used.

Influence of the Temperature on GZO Film Deposited by DC Magnetron Reactive Sputtering

GZO transparent conductive thin films were deposited by the direct current magnetron sputtering method from a ZnO target doped with Ga2O3 of 3wt% on glass slide substrates under high pressure of argon. The effect of substrate temperature on the GZO film’s morphology, optical and electrical properties is investigated by using scanning electron microscopy (SEM), UV spectrophotometer, four point probe and Spectroscopic Ellipsometer. The results showed that GZO thin films with high quality could be fabricated under the high pressure of argon.When substrate temperature is 250°C or below, surface morphology of thin films can be significantly improved.With the increase of substrate temperature, the crystal grain become larger, the crystal boundaries narrow and become clear, and reach a best case at 250°C. At the same time, the resistivity of GZO thin films decrease and reach the minimum which is 1.099×10-3 Ω•cm at 300°C while the average transmittance increase to 90%. Consequently, the properties of morphology began to get worse with the increase of temperature above 300°C.

Comparative Analysis of Al-Doped ZnO and Ga-Doped ZnO Thin Films

We have investigated the influences of aluminum and gallium dopants (0∼2.0 mol.%) on zinc oxide (ZnO) thin films regarding crystallization, electrical and optical properties for applications in transparent conducting oxide (TCO) devices. Al- and Ga-doped ZnO thin films were deposited on glass substrates. A lowest sheet resistance of 3.3 × 103 Ω/□ was obtained for the GZO thin film doped with 1.5 mol.% of Ga after post-annealing at 650 °C for 60 min in air. All the films showed more than 85% transparency in the visible region. We have studied the structural and microstructure properties as a function of Al and Ga concentration through X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. In addition, the optical bad gap (E g) and photoluminescence (PL) were estimated.

PES 기판위에 제작한 Ga-doped ZnO 박막의 전기적 및 광학적 특성

We fabricated gallium doped ZnO (GZO, 5 wt% Ga) thin films on PES (polyethersulfon) substrate with RF magnetron sputtering and investigated optical and electrical properties for various substrate temperatures (). All GZO thin film has c-axis preferred orientation without reference to deposition conditions. As a result of AFM analysis, the GZO thin film deposited at exhibited the lowest surface roughness of 0.196nm. The transmittance of GZO thin films were above 80% and Burstein-Moss effect was observed. In the analysis of Hall measurement, we confirmed that the GZO thin film deposited at showed the lowest resistivity of and the highest carrier concentration of .