Investigation of Electrophysical Properties of ITO Films
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PHYSICS OF SEMICONDUCTORS AND DIELECTRICS INVESTIGATION OF ELECTROPHYSICAL PROPERTIES OF ITO FILMS Yu. S. Zhidik,1,2 P. E.Troyan,1 V. V. Kozik,3 S. A. Kozyukhin,3,4 A. V. Zabolotskaya,3 and S. A. Kuznetsova3
UDC 537.9
The results of a study of the electrophysical characteristics of ITO films obtained by magnetron sputtering are presented. It is shown that a significant increase in the electrical conductivity of ITO films is facilitated by high-temperature annealing due to two processes. First, the high-temperature treatment of ITO films after their synthesis promotes the formation of a crystal structure, which leads to an increase in the mobility of charge carriers. Second, as a result of high-temperature annealing, the impurity in ITO films becomes completely electrically active, which leads to an increase in the concentration of conduction electrons and a change of the semiconductor mechanism of electrical conductivity to the metallic one. Keywords: ITO films, electrical conductivity, resistance, charge carrier mobility, charge carrier concentration.
INTRODUCTION At present, the characteristics of modern micro- and nanoelectronic devices are largely determined by the lowdimensional properties of semiconductor materials. Unlike traditional semiconductor materials, transition metal oxides possess a wider range of electrophysical properties, for example, a combination of high electrical conductivity and high transmittance coefficient in the visible range of the spectrum. Taking this into account, a new direction in the development of electronics based not on silicon, but on oxide semiconductor materials, – transparent electronics, is gaining more and more importance [1–3]. In this regard, investigation of electrical properties of transparent conducting metal oxides is an urgent task. The material of this class, currently most used in electronics, is thin films of tin-doped indium oxide (Indium Tin Oxide, ITO). Indium oxide relates to a degenerate n-type semiconductor [4] with a wide band gap (from 3.6 to 4.3 eV) and a degeneracy band width of (3–5) kT. The presence of a high concentration of conduction electrons in ITO films is due to the deviation of the film composition from stoichiometry [5]. Conduction electrons in such films are supplied from donor states associated with oxygen vacancies or an excess of metal ions [3]. The relatively low energy of formation of conventional transparent conducting oxides promotes a large oxygen deficiency even under the conditions of equilibrium growth [6]. In this case, the indium oxide formula can be written as In2O3–x(V)x, where V is a doubly charged donor-type oxygen vacancy supplying two free electrons to the conduction band. The values of the parameter x are usually less than 0.01 [7]. The concentration of free charge carriers is
1
Tomsk State University of Control Systems and Radioelectronics, Tomsk, Russia, e-mail: [email protected]; [email protected]; 2V. E. Zuev Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russi
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