Cadmium oxide, indium oxide and cadmium indate thin films obtained by the sol–gel technique M.A. Flores Mendoza a , R. Castanedo Pérez a, ⁎, G. Torres Delgado a , O. Zelaya Angel b a Centro de Investigación y de Estudios Avanzados del I. P.N., Unidad Querétaro, A.P.1-798, Querétaro, Qro. 76001, Mexico b Depto. de Física, Centro de Investigación y de Estudios Avanzados del I.P.N., A.P.14-740, Mexico 07360 D. F. Mexico abstract article info Available online 5 July 2009 Keywords: CdIn 2 O 4 films Sol–gel Transparent conductive oxides Thin films of the mixed CdO-In 2 O 3 system were deposited on glass substrates by the sol–gel technique. The precursor solution was obtained starting from the mixture of two precursor solutions of CdO and In 2 O 3 prepared separately at room temperature. The In atomic concentration percentages (X) in the precursor solution with respect to Cd (1 -X), were: 0, 16, 33, 50, 67, 84 and 100. The films were sintered at two different sintering temperatures (Ts) 450 and 550 °C, and after that, annealed in a 96:4 N 2 /H 2 gas mixture at 350 °C. X-ray diffraction patterns showed three types of films, excluding those constituted only of CdO and In 2 O 3 crystals: i) For X ≤ 50 at.%, the films were constituted of CdO + CdIn 2 O 4 crystals, ii) For X = 67 at.%, the films were only formed of CdIn 2 O 4 crystals and iii) For X = 84 at.% the films were constituted of In 2 O 3 + CdIn 2 O 4 crystals. In all films in the 0 b X b 100 range, the formation CdIn 2 O 4 crystals of this material was prioritized with respect to the formation of CdO and In 2 O 3 materials. All films showed high optical transmission and an increase of the direct band gap value from 2.4 (for CdO) to 3.6 eV (for In 2 O 3 ), as the X value increases. The resistivity values obtained were in the interval of 8×10 -4 Ω cm to 10 6 Ω cm. The CdIn 2 O 4 films had a resistivity value of 8×10 -3 Ω cm and a band gap value of 3.3 eV. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Thin films of cadmium indate (CdIn 2 O 4 ) have been studied in the last several years due to their various applications, such as: A trans- parent conductive oxide in solar cells [1], gas sensors [2,3], electrodes in biosensors [4] and transparent heat mirrors [5,6]. The crystal- lographic structure of CdIn 2 O 4 films generally corresponds to the cubic spinel phase. The films show an n-type semiconductor behavior, with resistivity values near to 10 -4 Ω cm [7] without additional doping and a wide optical bandgap around 3.2 eV [8]. Two techniques have mainly been used to deposit CdIn 2 O 4 thin films, rf sputtering [1,7,9] and dc reactive magnetron sputtering [8,10], and only in one study were these films deposited by pyrolysis, from organometallic indium and cadmium compounds in solution [11]. To the best of our knowledge, no attempt has been made to obtain CdIn 2 O 4 thin films using the sol– gel method. The sol–gel method offers several advantages such as: i) composition control, ii) homogeneity, iii) purity, iv) simplicity, v) the films are deposited starting from a precursor solution (no volatile toxic compounds) and vi) it is possible to cover large areas with irregular geometry. In this work, thin films of the mixed CdO-In 2 O 3 system were obtained with different indium atomic concentration percentages in solution, starting from the mixture of two precursor solutions CdO and In 2 O 3 by the sol–gel technique. The main objectives were to study the structural, optical and electrical properties of the multicomponent oxide films and to obtain CdIn 2 O 4 thin films. 2. Experimental details The CdO precursor solution was prepared starting from 1 mol of dehydrated cadmium acetate, 33 mol of methanol, 0.2 mol of glycerol, and 0.5 mol of triethylamine. The In 2 O 3 precursor solution was prepared using 1 mol of indium acetate, 90 mol of 1-propanol, 9 mol of lactic acid and 135 mol of deionized water. Both CdO and In 2 O 3 precursor solutions were obtained using simple procedures at room temperature (RT), which were previously reported by the authors [12,13]. The precursor solution of mixed CdO-In 2 O 3 was obtained by mixing both CdO and In 2 O 3 precursor solutions at RT, at different volumetric proportions, which were calculated to obtain the indium concentrations in the solutions of: 0,16, 33, 50, 67, 84 and 100 at.%. The films were deposited on glass slides as substrates at RT by the dipping method, after the final solution was obtained. The withdrawal speed was 10 cm/min. All the films were thermally pre-treated at 100 °C and sintered at two different sintering temperatures of 450 and 550 °C, in both cases in an air atmosphere for 1 h. All the films were obtained Thin Solid Films 518 (2009) 1114–1118 ⁎ Corresponding author. Tel.: +52 442 211 99 02; fax: +52 442 211 99 38. E-mail address: rcastanedo@qro.cinvestav.mx (R. Castanedo Pérez). 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2009.06.054 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf