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Carrier Transport in Homo- and Heteroepitaxial Zinc Oxide Layers

Published online by Cambridge University Press:  01 February 2011

Klaus Ellmer*
Affiliation:
ellmer@helmholtz-berlin.de, United States
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Abstract

Homo- and heteroepitaxial ZnMgO:Al, ZnCaO:Al and ZnO:Ga films have been grown on sapphire and ZnO substrates by RF (13.56 MHz) reactive magnetron sputtering from oxidic targets. The films grow epitaxially, i.e. with a preferred in-plane and out-of plane orientation. However, the heteroepitaxial films on sapphire exhibit a much higher crystallographic defect density, compared to the homepitaxial films. The ZnMeO films (Me – metal)on a-plane sapphire exhibit a lower defect density leading to higher Hall mobilities. Both, homo- and heteroepitaxial ZnO:Ga films with carrier concentrations N>1020 cm−3 exhibit the same mobility values, which increase with increasing carrier concentration. This behaviour is typical for electrical grain barrier limited transport, as decribed recently for polycrystalline ZnO:Al(Ga) films on glass. For the ZnCaO:Al films, deposited at similar conditions as the ZnO:Ga films, much lower carrier concentrations were measured, both for sapphire as well as for ZnO substrates. The mobilities of the ZnCaO:Al films on ZnO are much higher than that on the sapphire single crystals. The measured Hall mobilities are compared to single crystalline ZnO transport data.

Additionally, the work functions of the ZnMeO layers have been measured by X-ray and ultra-violet photoelectron spectroscopy. As expected, the work functions are lower compared to unalloyed ZnO, which can be used for ZnO band gap and band alignment engineering.

Type
Research Article
Copyright
Copyright © Materials Research Society 2009

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References

REFERENCES

[1] Özgür, U., Alivov, Y. I., Liu, C., Teke, A., Reshchikov, M. A., Dogan, S., Avrutin, V., Cho, S.-J., and Morkoc, H., J. Appl. Phys. 98, 041301–1…103 (2005).Google Scholar
[2] Transparent Conductive Zinc Oxide: Basics and Applications in Thin Film Solar Cells; Vol., edited by K. Ellmer, A. Klein, and B. Rech (Springer, Berlin, 2008).Google Scholar
[3] Ellmer, K., Electrical Properties, in Transparent Conductive Zinc Oxide: Basics and Application in Thin Film Solar Cells , edited by Ellmer, K., Klein, A., and Rech, B. (Springer, Berlin, 2008), p. 44.Google Scholar
[4] Galli, G. and Coker, J. E., Appl. Phys. Lett. 16, 439441 (1970).Google Scholar
[5] Ma, J., Li, F., Ma, H., and Li, S., Thin Solid Films 279, 213215 (1996).Google Scholar
[6] Igasaki, Y. and Saito, H., J. Appl. Phys. 69, 21902195 (1991).Google Scholar
[7] Cebulla, R., Wendt, R., and Ellmer, K., J. Appl. Phys. 83, 10871095 (1998).Google Scholar
[8] Minami, T., MRS Bull. 25, 3844 (2000).Google Scholar
[9] Ryu, Y. R., Zhu, S., Wrobel, J. M., Jeong, H. M., Miceli, P. F., and White, H. W., J. Cryst. Growth 216, 326329 (2000).Google Scholar
[10] Ohkubo, I., Ohtomo, A., Onishi, T., Matsumoto, Y., Koinuma, H., and Kawasaki, M., Surf. Sci. 443, L1043-L1048 (1999).Google Scholar
[11] Nakahara, K., Tanabe, T., Takasu, H., Fons, P., Iwata, K., Yamada, A., Matsubara, K., Hunger, R., and Niki, S., Jap. J. Appl. Phys. 40, 250254 (2001).Google Scholar
[12] Ellmer, K., J. Phys. D: Appl. Phys. 34, 30973108 (2001).Google Scholar
[13] Wendt, R. and Ellmer, K., Surf. Coat. Techn. 93, 2731 (1997).Google Scholar
[14] Handbook of Modern Ion Beam Materials Analysis; Vol., edited by J. R. Tesmer and M. Nastasi (MRS, Pittsburgh, 1995).Google Scholar
[15] Kuppusami, P., Vollweiler, G., Rafaja, D., and Ellmer, K., Appl. Phys. A 80, 183186 (2005).Google Scholar
[16] Ellmer, K. and Vollweiler, G., Thin Solid Films 496, 104111 (2006).Google Scholar
[17] Seto, J. Y., J. Appl. Phys. 46, 52475254 (1975).Google Scholar
[18] Ellmer, K. and Mientus, R., Thin Solid Films 516, 46204627 (2008).Google Scholar
[19] Makino, T., Segawa, Y., Tsukazaki, A., Ohtomo, A., and Kawasaki, M., Appl. Phys. Lett. 87, 022101–1…3 (2005).Google Scholar
[20] Makino, T., Segawa, Y., Tsukazaki, A., Ohtomo, A., and Kawasaki, M., phys. stat. sol (c) 3, 956959 (2006).Google Scholar
[21] Robertson, J., Xiong, K., and Clark, S. J., Thin Solid Films 496, 17 (2006).Google Scholar