Indium oxide and Sn-doped indium oxide
In2O3 is a wide band-gap material (fundamental gap of 2.9 eV, optical gap of 3.75 eV) with a bixbyite (closely related to fluorite) crystal structure. The unit cell of this material consists of 80 atoms which complicates a proper understanding of the doping mechanisms.
The research is focused on investigation of the effects of elevated temperatures on the impurities incorporation and their electrical activation in In2O3 matrix. Proper adjustment of the growth parameters allowed preparation of the tin-doped indium oxide (ITO) films with resistivity of 1.2x10-4 Ωcm  that is among the lowest values realized by magnetron sputtering, including non-reactive processes. The mobility value of 42 cm2 V-1 s-1 is comparable to the values achieved in ITO films grown by pulsed laser deposition. These properties combine with optical transmittance of the order of 90%.
Post-deposition thermal treatment is often necessary to improve electrical an optical properties of reactively sputtered ITO. Different methods, such as constant ramp, isothermal and electric current annealing of ITO films were investigated. Spectroscopic ellipsometry has been established as a real-time and contactless method for monitoring the free electron density in ITO [1-6]. This approach, in combination with in situ x-ray diffraction and resistivity measurements, provided direct evidence of tin-donor electrical activation during crystallization of amorphous ITO films [3-5]. Spectroscopic ellipsometry also allowed estimation of the Sn-donor activation rate in ultrathin epitaxial films of ITO . These results are complimentary to the data of x-ray photoelectron spectroscopy and scanning tunnelling microscopy.
BMBF Project 13N8053 "MF-Pulsed Dual Magnetron Sputter Deposition of ITO films", 2001-2003
SAB/SMWA Project 11815/1854 SOLARMETALL, 2006-2007
Fraunhofer Institut Elektronenstrahl und Plasmatechnik, Dresden
Partners from industry
1. A. Rogozin, M. Vinnichenko, N. Shevchenko, L. Vazquez, A. Mücklich, U. Kreissig, R.A. Yankov, A. Kolitsch, W. Möller: Effect of elevated substrate temperature on growth, properties, and structure of indium tin oxide films prepared by reactive magnetron sputtering. J. Mater. Res. 22, 2319 (2007).
2. A.I. Rogozin, M.V. Vinnichenko, A. Kolitsch, and W. Möller: Effect of deposition parameters on properties of ITO films prepared by reactive MF pulsed dual magnetron sputtering. J. Vac. Sci. Technol. A 22, 349 (2004).
3. A. Rogozin, N. Shevchenko, M. Vinnichenko, F. Prokert, V. Cantelli, A. Kolitsch, and W. Moeller: Real-time evolution of the indium tin oxide film properties and structure during annealing in vacuum. Appl. Phys. Lett. 85, 212 (2004).
4. A. Rogozin, N. Shevchenko, M. Vinnichenko, M. Seidel, A. Kolitsch, and W. Möller: Annealing of indium tin oxide films by electric current: properties and structure evolution. Appl. Phys. Lett. 89, 061908 (2006).
5. A. Rogozin, M. Vinnichenko, N. Shevchenko, U. Kreissig, A. Kolitsch, and W. Möller: Real-time evolution of electrical properties and structure of indium oxide and indium tin oxide during crystallization. Scr. Mater. 60, 199 (2009).
6. E.H. Morales, Y. He, M. Vinnichenko, B. Delley, and U. Diebold: Surface structure of Sn-doped In2O3(111) thin films by STM. New J. Phys. 10, 125030 (2008).