GZO Films Research Articles

Resistivity Stability of Ga Doped ZnO Thin Films with Heat Treatment in Air and Oxygen Atmospheres

The effect of annealing in air and oxygen on structural, electrical and optical properties of gallium doped ZnO thin films was investigated. The X-ray diffraction patterns showed that the films were highly preferentially oriented along (002) plane. After the heat treatment in air and oxygen environments, the intensity of (002) peak was apparently improved. It was found that heat treatment in air atmospheres lead to increase in surface roughness of the film. The GZO films annealed in oxygen at 673 K exhibited low resistivity of 4.21 × 10–3 Ω.cm, while the resistivity of film annealed in air showed a slightly higher value of 7.14 × 10–3 Ω.cm. In addition to this, all films have good optical transmittance about 80% in the visible region. It is found from the photoluminescence studies that the broad visible emissions in GZO films originated from the intrinsic shallow traps (VZn) and deep level vacancies (ZZi, OZn and Vo)

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

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

RF 마그네트론 스퍼터링법으로 증착한 태양전지용 GZO/ITO 투명전도성 박막의 물성에 미치는 ITO층의 영향

GZO/ITO double layered films were deposited on unheated non-alkali glass substrates by RF magnetron sputtering using an ITO (<TEX>$SnO_2$</TEX>: 10 wt%) and GZO(<TEX>$Ga_2O_3$</TEX>: 5.57 wt%) ceramic targets, respectively. The electrical resistivity of GZO/ITO films depends on the thickness ratio between the GZO film and ITO film. With increasing ITO film thickness, the resistivity of GZO/ITO films decreased which due to large increase in the Hall mobility. Also, the crystallinity of GZO/ITO film was improved with an increase in ITO thickness which was evaluated by X-ray diffraction. The average transmittance of the films was more than 85% in the visible region, which is slightly higher than ITO single layer films.

Effects of electron irradiation on the properties of GZO films deposited with RF magnetron sputtering

Transparent conductive GZO films were deposited on polycarbonate substrates by electron beam assisted radio frequency (RF) magnetron sputtering and then the influence of electron irradiation on the structural, optical and electrical properties of GZO films was investigated by using X-ray diffractometry, UV–vis spectrophotometry, four point probes, atomic force microscopy and UV photoelectron spectroscopy. Sputtering power was kept constant at 3W/cm2 during deposition, while electron irradiation energy varied from 450 to 900eV.Electron irradiated GZO films show larger grain sizes than those of films prepared without electron irradiation, and films irradiated at 900eV show higher optical transmittance in the visible wavelength region and lower sheet resistance (120Ω/□) than other films. The work-function is also increased with electron irradiation energy. The highest work-function of 4.4eV was observed in films that were electron irradiated at 900eV.

Development of all chemical solution derivedCe0.9La0.1O2 − y/Gd2Zr2O7 buffer layer stack for coated conductors: influence of the post-annealing process on surfacecrystallinity

Preparation and characterization of a biaxially texturedGd2Zr2O7 andCe0.9La0.1O2 − y (CLO, cap)/Gd2Zr2O7 (GZO, barrier) buffer layer stack by the metal–organic deposition route are reported.YBa2Cu3O7 − d (YBCO) superconductor films were deposited by the pulsed-laser deposition (PLD)technique to assess the efficiency of such a novel buffer layer stack. Biaxial texture qualityand morphology of the buffer layers and the YBCO superconductor films were fullycharacterized. The surface crystallinity of the buffer layers is studied by the electronbackscatter diffraction technique. It is revealed that post-annealing GZO films in2% H2 in Ar is an effective way to improve the surface crystallinity. As aresult, a highly textured CLO film can grow directly on the GZO filmat a lower crystallization temperature. The critical current density of aYBCOPLD film ishigher than 1 MA cm − 2 (@77 K, in self-field), demonstrating that the novel CLO/GZO stack is very promising forfurther development of low cost buffer layer architectures for coated conductors.

Ion sputter etching of ZnO:Ga thin film surfaces

In this article the modification of surface morphology of ZnO:Ga (GZO) thin films by ion sputter etching is presented. GZO thin films were prepared at room temperature on Corning glass substrates by both normal and oblique angle RF diode sputtering from ZnO:2%Ga ceramic target in Ar gas. Ion sputter etching was performed by RF re-sputtering of GZO thin films on substrates. During RF sputter etching, Ar pressure of 1.3Pa and RF power of 250W were kept constant, only the time of sputter etching was changed. Ion sputter etching had remarkable influence on surface morphology of GZO thin films: increase of roughness Rq and the “homogenization” of film surfaces, i.e. skewness (Rsk) and spikiness (Rku) parameters (Rsk≈0/Rku≈3).Surface root-mean-square roughness (Rq) increased from 15.3nm (after sputter deposition) to 29.1nm (after ion sputter etching). For obliquely thin films increased from 16.5nm (after sputter deposition) to 38.2nm. Changes of these parameters Rq, Rsk, Rku influenced optical properties of GZO films, increased Haze parameter up to values 7.7% and width of optical band gap 3.44eV, respectively.

Effects of sputtering power and pressure on properties of ZnO:Ga thin films prepared by oblique-angle deposition

The effects of power and pressure on radiofrequency (RF) diode sputtering in oblique-angle (80°) deposition arrangement are presented. Oblique-angle sputtering of ZnO:Ga (GZO) thin films resulted in a tilted columnar crystalline structure and inclination of the c-axis by an angle of approximately 9° with respect to the substrate. This improved their structural, electrical and optical properties in comparison with films deposited perpendicularly to the substrate. GZO films sputtered by an RF power of 600 W at room temperature of the substrate in Ar pressure 1.3 Pa showed strong crystalline (002) texture, lowest electrical resistivity 3.4 × 10 − 3 Ωcm, highest electron mobility 10 cm 2 V − 1 s − 1 , high electron concentration 1.8 × 10 20 cm − 3 and good optical transparency up to 88%. The small inclination angle of the film structure is caused by the high kinetic energy of sputtered species and additional energetic particle bombardment causes random surface diffusion, which is suppressing the shadow effect produced by oblique-angle sputtering.

P‐168: Room Temperature Deposition of Transparent Conducting Anode for Organic Light‐emitting Diodes

AbstractPoly‐crystalline Indium tin oxide (ITO) film, which shows high optical transmittance and low resistivity, is the essential material to realize OLED device as a transparent anodic electrode. However, this anode material has some problems for flexible displays or OLEDs due to the high manufacturing temperature and imperfect work function alignment in each layer of device. This study examined the anode material properties of ITO, GZO, and IZTO thin films deposited at room temperature using pulsed DC magnetron sputtering along with the device performance of organic emitting diodes (OLEDs). In conclusion, the IZTO film is an alternative material for conventional ITO anodes used in OLEDs and flexible displays.

Preparation of ZnO Based Thin Films for OLED Anode by Facing Targets Sputtering System

In this study, we prepared ZnO-based thin films-AZO, GZO and GAZO for OLED anode by facing targets sputtering (FTS) system. The reason of the used ZnO-based thin films is that it can be prepared to obtain high transparency in the visible range, low resistivity, stability of chemical and stability in hydrogen plasma by added materials such as Al, Ga. The electrical and optical properties of the as-doped AZO, GZO and GAZO thin films were evaluated with UV/VIS spectrometer, 4-point prove, XRD, AFM, FESEM. And the performance of the OLED device such as the operating voltage and its efficiency were evaluated by J-V-L (current density-voltage-luminance) measurements

Controlled Formation of ZnO Fine-Pattern Transparent Electrodes by Wet-Chemical Etching

Quality control of the chemicals used to form patterns in GZO films is very important when producing fine patterns. For example, using a TMAH (tetramethylammonium hydroxide) aqueous solution as a developer for a positive-type photoresist, precise control of its pH value in the range from 12.0 to 13.2 is essential when forming fine, dense patterns of lines and spaces a few micrometers wide in GZO films. A zinc-oxy-carbonate passivation layer was formed on the surface of GZO films by reaction with carbon dioxide absorbed from the atmosphere into the acid etchant. The passivation layer assisted the formation of a 2-μm-wide fine pattern because it reduced the etching rate of GZO in the acidic etchant

Enhanced infrared transmission of GZO film by rapid thermal annealing for Si thin film solar cells

ABSTRACTGa doped ZnO (GZO) films prepared by sputtering at room temperature were rapid thermal annealed (RTA) at elevated temperatures. With increasing annealing temperature up to 570°C, film transmission enhanced significantly over wide spectral range especially in infrared region. Hall effect measurements revealed that carrier density decreased from ∼8 × 1020 to ∼ 3 × 1020 cm−3 while carrier mobility increased from ∼15 to ∼28 cm2/Vs after the annealing, and consequently low film resistivity was preserved. Hydrogenated microcrystalline Si (µc‐Si:H) and microcrystalline Si1‐xGex (µc‐Si1‐xGex:H, x = 0.1) thin film solar cells fabricated on textured RTA‐treated GZO substrates demonstrated strong enhancement in short‐circuit current density due to improved spectral response, exhibiting quite high conversion efficiencies of 9.5% and 8.2% for µc‐Si:H and µc‐Si0.9Ge0.1:H solar cells, respectively. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Effect of Growth Conditions on Electronic and Structural Properties of GZO Films Grown by Plasma-enhanced Molecular Beam Epitaxy on p-GaN(0001)/Sapphire Templates

Abstract:We report on a strong effect of p-GaN surface morphology on the growth mode and surface roughness of ZnO:Ga films grown by plasma-assisted molecular-beam epitaxy on p-GaN/c-sapphire templates. A range of ZnO:Ga surface morphologies varying from rough surfaces with well defined three-dimensional islands, capable to enhance light extraction in light-emitting diodes, to rather smooth surfaces with a surface roughness of ~ 2 nm suitable for vertical-cavity lasers can be achieved by controlling the surface morphologies of p-GaN. Optical transmittance measurements revealed high transparency exceeding 90% in the visible spectral range for ZnO:Ga with both types of surface morphology.

Surface Characterization of Ga-doped ZnO layers

ABSTRACTEpitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400 °C under metaland oxygen-rich conditions in terms of metal-to-reactive oxygen ratio by plasma-assisted molecular beam epitaxy (MBE). Several atomic force microscopy (AFM) techniques were used to characterize the surface morphology and electrical properties of these GZO films in ambient conditions. Local I-V spectra indicate that layers grown under both O-rich and metal-rich conditions are highly resistive until a relatively high voltage sweep (±12 V) is used. After removal of an insulating surface layer, conduction is possible at lower voltages, but eventually the film resistivity increases and it again becomes insulating. In addition to local I-V spectra, local charge injection and subsequent surface potential measurements were used to probe surface charging characteristics. For charge injection experiments, a reverse-bias voltage is applied to the sample while scanning in contact mode with a metallized tip. The resultant change in surface potential due to trapped charge is subsequently observed using scanning Kelvin probe microscopy (SKPM). The layers deposited in a metal-rich environment demonstrate the expected behavior, but the O-rich layers show anomalous negative and positive charging. Finally, surface photovoltage (SPV) measurements using above-bandgap UV illumination were performed. The GZO layers produce SPV values of 0.4 to 0.5 eV, where the films deposited in an O-rich environment have slightly higher SPV values and faster restoration.

Electrical and optical properties dependence on evolution of roughness and thickness of Ga:ZnO films on rough quartz substrates

The paper studies GZO films deposited on quartz substrates by a laser deposition system. The XRD and AFM results as well as the calculation of height–height correlation function H (r, t) and its parameters w(t) and ξ(t) reveal that the film growth can be divided into two stages, and that the turning point of these two stages is the time when the film exhibits fractal characteristics. The influence of thickness and morphology roughness evolution on the electrical resistivity and optical transmittance in these two stages are described. It is found that the electrical resistivity mainly depends on the film thickness in the first stage, while in the following stage, the film possess self-affine fractal characteristics. The morphology roughness evolution plays an important role in the resistivity. The transmittance is found to decrease with the increase of film thickness in the two stages and it is also found to be sensitive to the evolution of surface roughness. The lowest resistivity obtained is 4.85×10−4Ωcm with an average optical transmittance of 85% in the 200nm thick film deposited for 10min.

Structure and properties of GZO thin films grown on ZnO buffer layers

Thin gallium-doped zinc oxide (in GZO the Ga 2O 3 contents are approximately 3 wt%) films having different ZnO buffer layers were deposited using radio frequency (rf) magnetron sputtering. The use of a grey-based Taguchi method to determine the processing parameters of ZnO buffer layer deposition has been studied by considering multiple performance characteristics. A Taguchi method with an L 9 orthogonal array, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) is employed to investigate the performance characteristics in the deposition operations. The effect and optimization of ZnO buffer deposition parameters (rf power, sputtering pressure, thickness, and annealing) on the structure, morphology, electrical resistivity, and optical transmittance of the GZO films are studied. Annealing treatment and reduction in thickness resulted in a decrease in root-mean-square (RMS) surface roughness of the ZnO buffer layer. Using the optimal ZnO buffer layer obtained by the application of the grey-based Taguchi method, the electrical resistivity of GZO films was decreased from 2.94×10 −3 to 9.44×10 −4 Ω cm and the optical transmittance in the visible region was slightly increased from 84.81% to 85.82%.

Effect of inserting a buffer layer on the characteristics of transparent conducting impurity-doped ZnO thin films prepared by dc magnetron sputtering

In transparent conducting impurity-doped ZnO thin films prepared on glass substrates by a dc magnetron sputtering (dc-MS) deposition, the obtainable lowest resistivity and the spatial resistivity distribution on the substrate surface were improved by a newly developed MS deposition method. The decrease of obtainable lowest resistivity as well as the improvement of spatial resistivity distribution on the substrate surface in Al- or Ga-doped ZnO (AZO or GZO) thin films were successfully achieved by inserting a very thin buffer layer, prepared using the same MS apparatus with the same target, between the thin film and the glass substrate. The deposition of the buffer layer required a more strongly oxidized target surface than possible to attain during a conventional dc-MS deposition. The optimal thickness of the buffer layer was found to be about 10 nm for both GZO and AZO thin films. The resistivity decrease is mainly attributed to an increase of Hall mobility rather than carrier concentration, resulting from an improvement of crystallinity coming from insertion of the buffer layer. Resistivities of 3 × 10 − 4 and 4 × 10 − 4 Ω cm were obtained in 100 nm-thick-GZO and AZO thin films, respectively, incorporating a 10 nm-thick-buffer layer prepared at a substrate temperature around 200 °C.

Structural, electrical and optical properties of Ga-doped ZnO films on PET substrate

The effects of O 2 plasma pretreatment on the properties of Ga-doped ZnO films on PET substrate were studied. Ga-doped ZnO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesion of PET substrate, O 2 plasma pretreatment process was used prior to GZO sputtering. With increasing O 2 plasma treatment time, the contact angle decreases and the RMS surface roughness increases significantly. The transmittance of GZO films on PET substrate in a wavelength of 550 nm was 70–84%. With appropriate O 2 plasma treatment, the resistivity of GZO films on PET substrate was 3.4 × 10 −3 Ω cm.

GZO/Metal/GZO 하이브리드 구조 투명 전도막의 전기적, 광학적 특성; Ag, Cu, Al, Zn 금속 삽입층의 효과

Transparent conducting films having a hybrid structure of GZO/Metal/GZO were prepared on glass substrates by sequential deposition using DC magnetron sputtering. Silver, copper, aluminum and zinc thin films were used as the intermediate metal layers in the hybrid structure. The electrical and optical properties of hybrid transparent conducting films were investigated with varying the thickness of metal layer or GZO layers. With increasing the metal thickness, hybrid films showed a noticeable improvement of the electrical conductivity, which is mainly dependent on the electrical property of the metal layer. GZO(40 nm)/Ag(10 nm)/GZO(40 nm) film exhibits a resistivity of <TEX>$5.2{\times}10^{-5}{\Omega}{\cdot}cm$</TEX> with an optical transmittance of 82.8%. For the films with Zn interlayer, only marginal reduction in the resistivity was observed. Furthermore, unlike other metals, hybrid films with Zn interlayer showed a decrease in the resistivity with increasing the GZO thickness. The optimal thickness of GZO layer for anti-reflection effect at a given thickness of metal (10 nm) was found to be critically dependent on the refractive index of the metal. In addition, x-ray diffraction analysis showed that the insertion of Ag layer resulted in the improvement of crystallinity of GZO films, which is beneficial for the electrical and optical properties of hybrid-type transparent conducting films.

Effect of composition and deposition temperature on the characteristics of Ga doped ZnO thin films

ZnO films doped with Ga (GZO) of varying composition were prepared on Corning glass substrate by radio frequency magnetron sputtering at various deposition temperatures of room temperature, 150, 250 and 400 °C, and their temperature dependent photoelectric and structural properties were correlated with Ga composition. With increasing deposition temperature, the Ga content, at which the lowest electrical resistivity and the best crystallinity were observed, decreased. Films with optimal electrical resistivity of 2–3 × 10 −4 Ω cm and with good crystallinity were obtained in the substrate temperature range from 150 to 250 °C, and the corresponding C Ga/( C Ga + C Zn) atomic ratio was about 0.049. GZO films grown at room temperature had coarse columnar structure and low optical transmittance, while films deposited at 400 °C yielded the highest figure of merit (FOM) due to very low optical absorption despite rather moderate electrical resistivity slightly higher than 4 × 10 −4 Ω cm. The optimum Ga content at which the maximum figure of merit was obtained decreased with increasing deposition temperature.

Effects of growth behaviors on chemical and physical properties of sol–gel derived ZnO:Ga films

In this study, we investigated the effects of different heating processes on the structural, electrical and chemical properties of ZnO:Ga (GZO) films from the viewpoint of nucleation and growth behaviors. An infrared heating furnace and a traditional tube furnace were employed for the homogeneous and heterogeneous nucleation of GZO films. XRD patterns demonstrated that the preferential growth orientation of both kinds of GZO films is still the (002) direction. XPS data implied that the infrared heating process enables more uniform distribution of the dopant material and retards the oxidization of gallium in grain boundary areas. At the same time, the textured crystallite might provide a free tunnel for oxygen diffusion. Thus, the activation of free charge carriers could be more efficient when the GZO films were annealed under vacuum. As a result, the samples annealed by the infrared heating furnace had a noticeably high carrier concentration. Although the mobility was slightly smaller than that of the samples annealed by the tube furnace, film resistivity dropped obviously in general.