ZnO is a very interesting material for range of applications in microelectronic, optoelectronic and photovoltaic devices. For example, it can be used as a transparent conductive oxide (TCO) film in blue light emitters, in UV light sensors and in solar cells [1]. In addition, ZnO doped with transition metal (TM – Co, Cu) ions is intensively studied for spintronics applications [2]. So the research on high-quality (Zn,TM)O alloy systems is becoming fairly important. Several reports suggest the important role of intrinsic defects [3,4], metal accumulations (Co clustering [5]), presence of uncompensated spins at surfaces of Co-rich regions [6], which may be of nm sizes and thus difficult to detect.

The presence of metallic TM inclusions is not visible in standard conductivity measurements, so in the present work we used the microwave conductivity (AC) method. This method is highly sensitive to such small inclusions. Therefore, AC measurements allow us to investigate uniformity of TM-distribution in (Zn,TM)O films, since the presence of metal inclusions results in large discrepancy between DC and AC conductivity.

In the present paper we demonstrate direct correlation between sample uniformity, Co/Cu concentration, growth parameters and AC conductivity of our films.

The project was financed by the National Science Centre granted based on the number of decision DEC-2013/09/N/ST5/00896.

[1] U. Ozgur, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Dogan, V. Avrutin, S.-J. Cho, and H. Morkoc, J. Appl. Phys. 98, 041301(2005).

[2] K. Sato, H. Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 40, L334 (2001).

[3] X. Zhang et al., Phys. Rev. B 80, 174427 (2009).

[4] J.M.D. Coey et al.,  J. Phys. D: Appl. Phys. 41, 134012 (2008).

[5] A. J. Behan et al., Phys. Rev. Lett. 100, 047206 (2008).

[6] M. Godlewski et al., Phys. Status Solidi (b) 248, 1596 (2011).

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