Transparent conductive oxides

ITO

Spatial distribution of the film electrical resistivity at different temperatures is investigated. The initial inhomogeneity of the resistivity over the non heated substrate (Figure 1) is caused by inhomogeneous plasma flow coming from each of two magnetrons and assisting deposition. Increase of the substrate temperature decreases spatial inhomogeneity and significantly decreases the film resistivity. At the temperature of higher than 400 °C the film resistivity reaches value of 1.2E-4 Ω •cm that is among the lowest values realized by magnetron sputtering, including non-reactive processes. The achieved Hall mobility value of 42 cm2•V-1•s-1 is comparable to the values achieved by pulsed laser deposition.

ITO 1

 

Figure 1. Spatial distribution of resistivity of the films grown at different substrate temperatures.

The real-time evolution of the film structure and properties is investigated in case of crystallization of amorphous ITO films during isothermal and electrical current annealing (Figure 2). In both cases the resistivity decreases in two stages. During the first stage (A) the film remains amorphous. The second stage (A → C) starts simultaneously with the crystallization outset and is accompanied with a strong increase of the free electron density due to Sn donor activation. Comparison of Arrhenius plots of the amorphous-to-crystalline transition rate for both isothermal and electric current annealing modes (Figure 3) shows lower activation energy of the crystallization at electrical current annealing. This method is advantageous for annealing of the ITO films grown on thermally sensitive substrates.

 
 

Figure 2. Real-time evolution of the film structure, electrical resistivity and free electron density during annealing by electrical current.

ITO 2

Figure 3. Arrhenius plots of the amorphous-to-crystalline transition rate for isothermal and electric current annealing modes.

 
ITO 3

ZnO:Al

The effect of ion implantation by Al+ ions on ZnO film structure, electrical and optical properties has been studied. Al incorporated in polycrystalline ZnO thin films by ion implantation shows electrical activation below 20%. The main effects of the Al ion implantation on the film optical properties are the band gap widening (Figure 5). The free electron density increase has the main contribution to the band gap widening at the implantation dose larger 2×1016 cm-2, while at lower doses effect of tensile stress accumulation has to be additionally considered.

Figure 4. Dependence of the ZnO band gap shift on the free electron density determined experimentally and calculated according to the Burstein-Moss model. ZnO:Al

Publications

1. A. Rogozin, M. Vinnichenko, N. Shevchenko, L. Vazquez, A. Mücklich, U. Kreissig, R.A. Yankov, A. Kolitsch, and W. Möller: The effect of elevated substrate temperature on the growth, properties and structure of indium tin oxide films prepared by reactive magnetron sputtering, J. Mater. Res. 8 (2), (2007) (in press).

2. 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).

3. A. Rogozin, M. Vinnichenko, N. Shevchenko, A. Kolitsch, and W. Moeller: Plasma influence on the properties and structure of indium tin oxide films produced by reactive middle frequency pulsed magnetron sputtering, Thin Solid Films 496, 197 (2006).

4. A. Rogozin, N. Shevchenko, M. Vinnichenko, F. Prokert, V. Cantelli, A. Kolitsch, and W. Moeller: Real-time evolution of the ITO film properties and structure during annealing in vacuum, Appl. Phys. Lett. 85, 212 (2004).

5. 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).