Molybdenum doped Indium Oxide thin films prepared by rf sputtering
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Molybdenum doped Indium Oxide thin films prepared by rf sputtering E. Elangovan, A. Marques, A. Pimentel, R. Martins and E. Fortunato Department of Materials Science/CENIMAT, Faculty of Sciences and Technology, New University of Lisbon and CEMOP-UNINOVA, 2829-516 Caparica, Portugal Tel: +351212948562; Fax: +351212948558; e-mail: [email protected] ABSTRACT Molybdenum doped indium oxide (IMO) thin films rf sputtered at room temperature were studied as a function of oxygen volume percentage (O2 vol. %) varied between 0 and 17.5. The as-deposited films were amorphous irrespective of O2 vol. %. The minimum transmittance (300 °C) tend to show the characteristic broad peak of amorphous structure. Annealing at 200 °C has been effective to crystallize the films only those deposited without oxygen. Whereas films annealed at 100 °C retained the amorphous structure irrespective of deposition and annealing conditions. When the O2 vol. % increased above 3.5 the films crystallize feebly by retaining the characteristic amorphous broad peak irrespective of annealing conditions; the films annealed at high temperatures in N2/H2 gas show additional peaks such as (321), (411) and (640). However, the films annealed at 300 °C shows stability in crystallization irrespective of the deposition and annealing conditions. The foregoing discussion shows that the minimum O2 vol. % (3.5) and the annealing temperature of 300 °C are the best conditions to obtain quality films. Optical properties The optical transmittance spectra recorded in the wavelength between 300-2500 nm for the films deposited with 0.0 and 3.5 O2 vol. % are shown in Figs. 3 & 4 respectively. The
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Figure 1. XRD patterns of films deposited with 0.0 O2 vol. %; annealed at different temperatures in (a) open air, and (b) N2/H2 gas.
Figure 2. XRD patterns of films deposited with 3.5 O2 vol. %; annealed at different temperatures in (a) open air, and (b) N2/H2 gas. subsections (a) and (b) represent the annealing air and N2/H2 gas respectively. A bare substrate was placed in the path of reference beam and thus the transmittance is only due to the material. The minimum transmittance (7 % at 570 nm) of films as- deposited (brown color) without
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oxygen (Fig. 3) has been increased to a maximum of 84 % on annealing at 300 °C (colorless) irrespective of annealing atmospheres; although, the transmittance of the films annealed at 500 °C in open air is slightly higher (86 %), it has been dropped considerably (silver color) when annealed in N2/H2 gas (2 %). On the other hand, the transmittance of the films as- deposited with minimum O2 vol. % (3.5) increased tremendously (Fig. 4a) to a maximum of 90 % at 600 nm and was maintained irrespective of annealing temperatures; however, the transmittance has been decreased considerably when annealed at high temperatures (dark brown color) in N2/H2 gas (Fig. 4b). The films deposited with > 3.5 O2 vol. % showed the same trend but the visible transmittance has been dropped below 80 % when annealed
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