Electron–Electron Interactions in Sb-Doped SnO 2 Thin Films TU ¨ LAY SERIN, 1 ABDULLAH YILDIZ, 1,2,4 NECMI SERIN, 1 NURCAN YILDIRIM, 1 FIGEN O ¨ ZYURT, 1 and MEHMET KASAP 3 1.—Department of Physics Engineering, Faculty of Engineering, Ankara University, 06100 Besevler, Ankara, Turkey. 2.—Department of Physics, Faculty of Science and Arts, Ahi Evran University, 40040 Kirsehir, Turkey. 3.—Department of Physics, Faculty of Science and Arts, Gazi University, Teknikokular, 06500 Ankara, Turkey. 4.—e-mail: yildizab@gmail.com Electrical conductivity and Hall-effect measurements on undoped and Sb-doped SnO 2 thin films prepared by the sol–gel technique were carried out as a function of temperature (55 K to 300 K). Structural characterizations of the films were performed by atomic force microscopy (AFM) and x-ray diffraction (XRD). A doping-induced metal–insulator transition (MIT) was observed. On the metallic side of the transition, the experimental data were interpreted in terms of electron–electron interactions (EEI). The existence of EEI was confirmed by excellent agreement between theoretical and experi- mental data. The experimental data on the insulator side of the transition were analyzed in terms of variable-range hopping (VRH) conduction. A com- plete set of parameters describing the properties of the localized electrons, including hopping energy, hopping distance, and the value of the density of states at the Fermi level, was determined. Key words: SnO 2 , electrical transport, electron–electron interactions (EEI), variable-range hopping (VRH) conduction INTRODUCTION Tin oxide (SnO 2 ), with a wide bandgap of 3.6 eV, is an n-type metallic oxide semiconductor material of great interest due to its numerous technological applications in gas sensors and solar cells. 1,2 Recently, many reports have been published on metallic oxide semiconductors such as titanium oxide (TiO 2 ) and SnO 2 . 3–9 However, most of these studies are generally concerned with structural and optical properties. Generally, the electrical proper- ties of SnO 2 are investigated by experimental direct- current (DC) conductivity data on different doped samples. The electrical conductivity of SnO 2 can be chan- ged by doping over several orders of magnitude. Control of the electrical conductivity of SnO 2 by adding antimony (Sb) as a donor impurity is a well- known process. At low Sb doping levels, the [Sb 5+ ] state in SnO 2 leads to an increase in conductivity. 7 On the other hand, the Hall mobility of SnO 2 decreases significantly from 5 cm 2 V –1 s –1 to 0.1 cm 2 V –1 s –1 at high Sb doping levels. 7 The Hall carrier concentration is generally of the order of 10 20 cm 3 for any Sb doping level in SnO 2 . 7 The increase in carrier concentration in SnO 2 is caused by replacement of a Sn atom by an added Sb atom, which gives one extra charge carrier 8 per donor impurity. The physical properties of SnO 2 films also depend on the preparation technique. Although the sol–gel process has many advantages over other tech- niques, it is hard to correlate the optical and elec- trical properties of SnO 2 films made using this process. 9 Thus, to understand the nature of the charge transport behavior of SnO 2 , it is necessary to perform a thorough investigation. In order to observe the metal–insulator transition (MIT) in a material, it is generally necessary to add doping, which results in the formation of a degen- erate band. 10 Conductivity changes significantly when the MIT is reached. It is possible that dis- ordered metallic conduction can be observed due to the presence of various types of disorder in highly (Received November 25, 2009; accepted April 18, 2010; published online May 22, 2010) Journal of ELECTRONIC MATERIALS, Vol. 39, No. 8, 2010 DOI: 10.1007/s11664-010-1252-y Ó 2010 TMS 1152