Mechanism of electrical properties degradation of ZnO:Al films during growth at elevated temperatures


Mechanism of electrical properties degradation of ZnO:Al films during growth at elevated temperatures

Vinnichenko, M.; Gago, R.; Cornelius, S.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Möller, W.

Resistivity of ZnO:Al (AZO) films is known to increase significantly during annealing or growth at temperatures higher than certain optimum value that is a problem during preparation of thin film solar cells. To understand this process, AZO films with different Al concentrations grown by reactive pulsed magnetron sputtering were studied. The electrical resistivity of the films shows a minimum at an optimum substrate temperature, which shifts from 400 °C to 200 °C with increasing Zn/O flux ratio. At higher temperatures, resistivity increases due to simultaneous decrease of the free electron density and mobility. It is accompanied by a significant deterioration of the film crystallinity, increase of Al concentration and drop of the growth rate. X-ray absorption near edge structures (XANES) excludes formation of aluminum oxides in this case. It shows formation of homologous phase (ZnO)3(Al2O3) whose formation is triggered by an increase of the Al/Zn ratio in the film. Therefore, at growth temperatures above the optimum value Al preferentially forms this phase instead of occupying Zn site in the lattice.

Keywords: Al-doped ZnO; transparent conductive oxides; homologous metastable phase; (ZnO)3(Al2O3)

  • Lecture (Conference)
    5th Forum on New Materials (in the framework of 12th International Conference on Modern Materials and Technologies - CIMTEC 2010), 13.-18.06.2010, Montecatini Terme, Italy

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Publ.-Id: 14205