International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Special Issue: 09 | Sep -2017
p-ISSN: 2395-0072
www.irjet.net
One Day International Seminar on Materials Science & Technology (ISMST 2017) 4th August 2017 Organized by
Department of Physics, Mother Teresa Women’s University, Kodaikanal, Tamilnadu, India
Indium doped Zinc oxide thin films: Effect on structural, optical and electrical characteristics. A. Jacquiline Regina Mary1, S.Arumugam2 Department of Physics, Jayaraj Annapackiam College for Women (Autonomous), Periyakulam, Theni Dist, Tamilnadu, India. 2 Solar Energy Division, Department of Physics, The Gandhigram Rural Institute-Deemed University, Gandhigram, Dindigul Dist, Tamilnadu, India. ---------------------------------------------------------------------***--------------------------------------------------------------------1
Abstract - The effect of Indium doping on the structural,
prepare quality films. Chemical spray pyrolysis (CSP) is the method used to deposit TCO earlier; even now it continues to be the easier deposition technique for large scale production and cost effective[4-6].
optical and electrical properties of Zinc oxide thin films (IZO) prepared through spray pyrolysis method is reported. The dopant concentration was varied as 1, 2, 5 and 7.5 taken in mole percentage. XRD analysis show that the average grain size of IZO thin films decreases as the dopant concentration increases. When doped heavily, the optical band gap (Eg) was found to increase from 3.06 eV to 3.6 eV, which is due to Burstein-Moss effect. The optical constants such as refractive index (n) and extinction co-efficient (k) are calculated from the reflectance and UV-absorbance data respectively. FTIR studies revealed the formation of Zn-O bond at 489 cm-1.The overall transmittance of the IZO films are found to be above 83% in the visible and near IR region. There is a blue emission centered around 458 nm in the PL emission spectra. It is found that electrical conductivity (σ) is enhanced due to doping by observing the Four probe measurements. The optical and electrical properties of Indium doped ZnO thin films prove it to be a suitable candidate for making transparent electrodes in solar cell.
Zinc oxide is highly resistive in its pure form and efforts are made by researchers to improve its electrical conductivity by intentional doping. Selection of the dopant should be based on the ionic size and electro negativity, since these two factors decide the efficiency of the dopant element. High valence group III elements are chosen to enhance the electrical properties of ZnO. Among those aluminum (AZO) and gallium (GZO) doped ZnO are studied much. There are only few reports on Indium doped ZnO (IZO). Indium doping lowers the resistivity of the films, with values ranging from 4.03x 10-5 to 3x10-3 Ω cm [7,8]. The present work is aimed at synthesizing good quality films for their application as transparent electrode in solar cells. The optimized zinc oxide thin films are doped with indium and its effect on the structural, optical and electrical properties of ZnO thin films are investigated.
Key Words: Grain size, optical band gap, transmittance, refractive index, electrical conductivity.
1.1 Materials and methods
1. INTRODUCTION
Zinc acetate [Zn (CH3 COO)2 . 2H2O] and Indium chloride (In Cl3) are the precursor materials purchased from Sigma Aldrich(99%), which are dissolved in Isopropyl alcohol and de-ionized water in the ratio 3:1. The films are deposited on to precleaned brosilicate glass substrate 1mm thick. Few drops of acetic acid were added to improve the solubility of Zinc acetate and Indium chloride mixture in the solvent. The resultant solution was stirred at 60˚C for 1 h to yield a clear homogenous solution, which is used for coating. After coating, the In doped ZnO (IZO) films were allowed to cool to room temperature. The films were post annealed at 773K for 1 hour.
Zinc oxide based thin films are better choice to ITO due to their excellent electrical and optical properties in the visible region. Zinc oxide is an extensively studied material, since it's electrical conductivity can be made high with high visible transmittance. It has a wide band gap of 3.37eV and exciton binding energy of 60mev. Transparent conductive oxide (TCO) such as ITO, ZnO thin films find applications in optoelectronic devices like solar cells, flat panel displays (eg touch panel displays), Organic light emitting diodes (OLED), and low e- windows [1-3]. Since vacuum techniques require sophisticated instruments and maintenance, because of its simplicity, chemical methods draw attention in the synthesis of good films. But both physical and chemical deposition techniques could be employed based on the requirement to © 2017, IRJET
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