Processing and Study of Optical and Electrical Properties of (Mg, Al) Co-Doped ZnO Thin Films Prepared by RF Magnetron Sputtering for Photovoltaic Application (original) (raw)
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Journal of Materials Science: Materials in Electronics
In this research, AZO thin films were deposited on glass substrates with 70 W, 100 W and 125 W RF powers at room temperature by RF magnetron sputtering technique. The structural, optical and surface properties of the produced thin films were investigated. According to the obtained results, the investigated thin films had a crystalline structure and they showed high transparency in the visible region. The increase of RF power produced thicker films. Relatively thicker AZO films produced with higher RF power exhibited greater number of interference fringes in the reflectance and transmittance spectra. The refractive index values of the film produced with 125 W RF power were considerably lower than those of the films produced with 70 W and 100 W due to the decreased packing density. The optical energy band gap values of the produced AZO thin films were higher than that of undoped ZnO films. This expansion resulted from the Burstein-Moss effect. However, the band gap energy value as well as the roughness of the film surface decreased like refractive index with an increase in RF power, especially after 100 W. As a result, the values corresponding to the optical and surface properties can be tuned and AZO thin films can be produced by RF magnetron sputtering technique as promising candidates for optoelectronic devices and transparent conductive oxide applications.
Keywords: Al–F co-doped ZnO Transparent conducting oxide (TCO) Thin film magnetron sputtering Substrate temperature a b s t r a c t ZnO is a wide bandgap semiconductor that has many potential applications such as solar cells, thin film transistors, light emitting diodes, and gas/biological sensors. In this study, a composite ceramic ZnO target containing 1 wt% Al 2 O 3 and 1.5 wt% ZnF 2 was prepared and used to deposit transparent conducting Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering. The effect of substrate temperatures ranging from room temperature (RT) to 200 • C on structural, morphological , electrical, chemical, and optical properties of the deposited thin films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Hall effect measurement, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and UV–vis spectrophotometer. The XRD results showed that all the AFZO thin films had a (0 0 2) diffrac-tion peak, indicating a typical wurtzite structure with a preferential orientation of the c-axis perpendicular to the substrate. The FE-SEM and AFM analyses indicated that the crystallinity and grain size of the films were enhanced while the surface roughness decreased as the substrate temperature increased. Results of Hall effect measurement showed that Al and F co-doping decreased the resistivity more effectively than single-doping (either Al or F doping) in ZnO thin films. The resistivity of the AFZO thin films decreased from 5.48 × 10 −4 to 2.88 × 10 −4-cm as the substrate temperature increased from RT to 200 • C due to the increased carrier concentration and Hall mobility. The optical transmittances of all the AFZO thin films were over 92% in the wavelength range of 400–800 nm regardless of substrate temperature. The blue-shift of absorption edge accompanied the rise of the optical band gap, which conformed to the Burstein-Moss effect. The developed AFZO thin films are suitable as transparent conducting electrodes for various optoelectronic applications.
Journal of Alloys and Compounds, 2017
In the present work, we have deposited Ga-doped ZnO (GZO) thin films by magnetron sputtering technique using nanocrystalline particles elaborated by sol-gel method as a target material. The effect of the thickness, on the physical properties of the GZO thin films was analyzed. The influence of the thickness, on structure, surface morphologies, chemical atomic composition, electrical and optical properties was investigated by XRD, SEM, TEM, AFM, Raman measurement, Hall measurement and UV Vis-NIR spectrophotometer, respectively. X-ray diffraction (XRD) results revealed the polycrystalline nature of the films with hexagonal wurtzite structure having preferential orientation a long [002] direction normal to the substrate. The lowest resistivity obtained from electrical studies was 10-4 Ω cm. The optical properties were studied using a UV-vis spectrophotometer and the average transmittance in the visible region (400-800 nm) was found to be 90 %.
Research & Reviews Journal of Material Sciences, 2018
Zinc oxide (ZnO) is a semiconducting material with more important and interesting properties than most other materials. It is a II-VI compound semiconductor whose ionicity resides at the borderline between the covalent and ionic semiconductors. The significant properties of ZnO are: a direct band gap (3,4 eV) at room temperature, high exciton binding energy (60 meV) [1] , which is much greater than ZnSe (20 meV) and GaN (25 meV), high optical transparency in the visible region and low electrical resistivity. The higher exciton binding energy enhances the luminescence efficiency. Non-toxicity and abundance of ZnO on earth makes it an ideal candidate used as a transparent electrical contact for solar cells in thin layers. Owing to these properties, ZnO becomes a very promising material for many practical applications such as a transparent conductive contact [2] , thin films gas sensors [3,4] , varistors [5] , surface acoustic wave devices [6] , U.V laser [7] , luminescent materials [8] , an n-type conducting window in thin film solar cells based on cadmium telluride [9] or indium diselenide [10] and others. Several technics have been used for fabrications of ZnO thin films such as physical vapor deposition (PVD) [11] , magnetron sputtering [12] , spray pyrolysis [13] , Chemical vapor deposition (CVD) [14] electrochemical deposition and sol-gel processing [15]. Among these technics, sol-gel attracted more interests because of its great advantages: simplicity, low cost, large area substrate ABSTRACT Aluminium doped and (Mg-Al) co-doped zinc oxide thin films were deposited by sol-gel technic from aqueous solution onto glass substrates at optimum conditions. The variations of the structural, electrical and optical properties with the doping and co-doping concentration were investigated. XRD analysis showed typical patterns of the hexagonal ZnO structure for all films and AMZO thin films exhibited preferred orientation growth along the c-axis. No diffraction peaks of any other structure were found. The grain size, texture coefficient and optical band gap values were evaluated for different aluminum concentrations and (Mg-Al) co-doping ratio. The results show that increasing the Mg content, the films improve their crystallinity with the (002) preferred orientation and the transmittance reaches 85%. The optimized results were obtained for co-doped (Mg-Al) concentration at ratio of 2/1.
Thin Solid Films, 2010
Transparent conducting oxide Mo-doped ZnO (ZnO:Mo) Thin film Pulsed direct current magnetron sputtering The purpose of this study is to use pulsed magnetron sputtering to deposit transparent conductive ZnO:Mo (MZO) film on a Corning 1737 glass substrate. Various process parameters, including power, work pressure, pulsed frequency, film thickness, and substrate temperature, were analyzed for their effects on the microstructure and optoelectronic characteristics of MZO thin film. Experimental results show that MZO film with a low resistivity of approximately 8.9 × 10 − 4 Ω cm and a visible light transitivity of greater than 80% can be obtained using a Mo content of 1.77 wt.%, sputtering power of 100 W, work pressure of 0.4 Pa, pulsed frequency of 10 kHz, and film thickness of 500 nm without heating. The value of optical band gap of MZO increased upon increasing the crystallinity of the MZO thin film, and the range of the optical band gap of MZO thin film is from 3.30 to 3.35 eV.
Thin Solid Films, 2008
Metal doped ZnO (MZO, metal = Al, Ag, Li) films were deposited by RF magnetron sputtering system. We investigated the physical properties and the etching characteristics of the MZO films. All MZO films have shown a preferred orientation in the [001] direction. As amounts and a kind of dopant in the target were changed, the crystallinity and the transmittance as well as the optical band gap were changed. The electrical resistivity was also changed according to the metal doping amounts and a kind of dopant. The chemical dry etching of as-grown MZO thin films was investigated by varying gas mixing ratio of CH 4 /(CH 4 + H 2 + Ar) and additive Cl 2 chemistries. We could effectively etch not only a zinc oxide but also metal dopant using methane, hydrogen, argon, as well as chlorine gas. Changes of the structural, optical electrical properties, etch rate, and chemical states of etched surface for the MZO films were also explained with the data obtained by SEM, XRD, UV, 4-point-probe and XPS analyses.
Structural and optical properties of Al-doped ZnO thin films produced by magnetron sputtering
Processing and Application of Ceramics
Experimental and theoretical investigations of the structure and optical properties of Al-doped ZnO (AZO) thin films produced by magnetron sputtering under different values of electric current were conducted. The XRD results confirm the formation of the AZO thin films with hexagonal wurtzite structure, with preferential orientation along the crystallographic plane (002), direction c. The increment of electric current allowed an increase in average crystallite size. The FE-SEM and AFM images analyses of the AZO films revealed the occurrence of nucleation on the substrate surface that formed films with granular and rough structure. The higher substrate temperature caused by the higher value of electric current had influence on the grain size and thickness (ranging from 974 to 1500 nm) of the formed thin films. Due to the high absorption of free carriers, the optical transmittance of the AZO films was acceptable for the visible spectrum and limited to the near infrared region. The ener...
Magnetron sputtered Al-ZnO thin films for photovoltaic applications
The optimization process of the RF magnetron sputtered Aldoped ZnO (AZO) thin films was carried out by studying its structural, optical, electrical, and morphological properties at different RF power and different working pressures for its use as a front-contact for the copper indium diselenide (CIS) based thin film solar cell. The structural study suggests that the preferred orientation of grains along the ( 002) plane having a hexagonal structure of the grains. The optical and electrical properties suggest that the films show an average transmission of 85 % and a resistivity of the order of 10 -4 Wcm. The morphology analysis suggests the formation of packed grains having a homogeneous surface.
Temperature dependent studies on radio frequency sputtered Al doped ZnO thin film
Engineered science, 2020
In this work, highly conductive and transparent Al: ZnO (Al doped ZnO, i. e., AZO) thin films were grown by radio frequency (RF) magnetron sputtering technique at a typical deposition temperature. The effect of deposition temperature on the structural, morphological, optical and electrical properties was studied. The x-ray diffraction (XRD) studies revealed a hexagonal wurtzite crystal structure for all AZO layers with a (002) preferred orientation along the c-axis. Columnar, compact, uniform grain growth of the layer was observed from atomic force microscopy (AFM) images. The deposition temperature had an influence on the surface roughness and average grain size of deposited films, which could be confirmed by means of AFM images. Optical studies confirmed that both optical band gap energy and urbach energy were influenced by the substrate temperature. Highly transparent films with an energy band gap ranging from 3.48 to 3.65 eV were obtained upon changing the deposition temperature from 22 to 400. The presence of defects was confirmed by ℃ photoluminescence (PL) spectra. A systematic measurement of the electrical parameters like barrier height, and ideality factor of the devices (Ag/Al:ZnO) was carried out with the help of I-V characteristic. This study may be useful for the design and fabrication of AZO based electrodes for solar cell applications.