INVESTIGATION OF CO EFFECT ON THE TEMPERATURE DEPENDENT OF THE

Abstract

The Co effect on the temperature dependent electrical properties of ZnO thin films was examined. The ultrasonic spray pyrolysis technique were used for Co doped ZnO thin films on glass substrates prepared with cobalt at different concentrations. The effects of Co doping on the structural, optical and electrical properties of ZnO were investigated using with the results of x-ray diffraction (XRD), scanning electron microscope (SEM), EDX, optical transmittance measurements and electrical conductivity measurements. In the structure of Co doped ZnO samples, it is dominantly observed hexagonal wurtzite structure of ZnO. The effect of Co ions intercalated into ZnO crystal structure has been observed by examining the cubic phase of cobalt oxide in XRD difractograms and differences in the reflection peak (200) intensity. Phase changes of Co doped ZnO has been found to be controlled by the amount of Co. In the samples, Co threshold concentration value was determined by EDS analysis. The existence of Co in ZnO lattice has been proved by the Co2+characteristics as d-d transitions observed in the optical transmittance spectrum. The temperature dependent current of the samples are consistent with the electrical behavior of ZnO as the host material. All the films showed the single activation energy type behavior obtained from the dark conductivity measurement using lnk-1/T variation in the high temperature region. The single type of activation energy due to the increase of the Co content shows that a tendency to decrease after the critical value of Co molarity in the precursor solution

Keywords

• ZnO, Co doping, electrical conductivity, ultrasonic spray pyrolysis technique

ZNO İNCE FİLMLERİN SICAKLIĞA BAĞLI ELEKTRİKSEL DAVRANIŞINDA CO ETKİSİNİN İNCELENMESİ

Abstract

ZnO ince filmlerin sıcaklığa bağlı elektriksel özelliklerinde Co etkisi incelenmiştir. Cam alttaş üzerine, farklı Co molaritelerinde hazırlanan Co katkılanmış ZnO ince filmler için ultrasonik kimyasal püskürtme tekniği (UKP) kullanılmıştır. Co katkısının ZnO ince filmlerin yapısal, optiksel ve elektriksel özelliklerine etkisi x-ışını kırınım (XIK), taramalı elektron mikroskopu (SEM), EDS, optiksel geçirgenlik ve elektriksel iletkenlik ölçüm sonuçları ile değerlendirilmiştir. Co katkılı ZnO örneklerin yapısında, ZnO’e ait hekzagonal wurtzit yapının baskın olduğu gözlenmiştir. ZnO kristal yapısına giren Co iyonlarının etkisi, XIK desenlerinde kobalt oksite ait kübik fazın (200) yansıma pikindeki şiddet farkının ortaya çıkmasıyla gözlenmiştir. Co katkılı ZnO yapıdaki faz değişiminin, Co miktarı ile kontrol edildiği anlaşılmıştır. Örneklerdeki Co’ın eşik konsantrasyon değeri EDS analizi ile belirlenmiştir. ZnO örgüsü içindeki Co’ın varlığı, optik geçirgenlik spektrumlarındaki Co+2 iyonuna ait karakteristik d-d geçişlerinin gözlenmesiyle kanıtlanmıştır. Co katkılı ZnO örneklerin sıcaklığa bağlı akım değişimleri, ana malzeme olan ZnO’in davranışı ile uyumludur. Karanlık iletkenliklerinden elde edilen lnk-1/T grafiğinde, yüksek sıcaklık bölgesinde aktivasyon türü davranış gözlenmektedir. Artan Co miktarı ile tek tür aktivasyon enerjisinde gözlenen artış, Co’ın başlangıç ön çözelti molaritesindeki kritik değerden sonra azalma eğilimi göstermektedir

Keywords

• ZnO, Co katkılama, elektriksel iletkenlik, ultrasonik kimyasal püskürtme tekniği

References

1. Ismail, B., Abaab, M., and Rezig, B. 2001. Structural and electrical properties of ZnO films prepared by screen printing technique, Thin Solid Films, Cilt. 383, s.92-94. DOI: 10.1016/S0040-6090(00)01787- 9
2. Gungor, E., Gungor, T. 2012. Effect of the substrate movement on the optical properties of ZnO thin films deposited by ultrasonic spray pyrolysis, Advances in Materials
3. Engineering, Article ID 594971. DOI: 10.1155/2012/594971
4. and [3] Ueda, K., Tabata. H., and Kawai, T. 2001. Appl. Phys. Lett. Cilt. 79, s. 988-990.DOI: 10.1063/1.1384478 [4] Cho, Y.M., Choo, W.K., Kim H, and Ihm, Y.E. 2001. Appl. Phys. Lett. Cilt. 10.1063/1.1478146
5. DOI: [5] Lee, H.J., Jeong, S.Y., Cho, C.R., and Park C.H. 2002. Appl. Phys. Lett. Cilt. 81, s. 4020-4022. DOI: 10.1063/1.1517405
6. Lee, H.J., Kim, S.K., Cho, C.R., Kim, S.J., and Jeong, S.Y. 2005. J. Korean Phys. Soc. Cilt. 46, s. 34.
7. Rode, K., Anane, A., and Contuor, J. P. 2003. J. Appl. Phys. Cilt. 93, s. 7676. DOI: 10.1063/1.1556115
8. Olvera, M.L., Maldonado, A., and Asomoza, R. 2002. ZnO:F thin films deposited by chemical spray: effect

9. concentration in the starting solution, Sol. Energ. Mater. Sol. C., Cilt. 73, No. 4, s.425-433. DOI: 10.1016/S0927-0248(02)00211- 8
10. fluorine [9] Kim, J.H., Kim, H., Kim, D., Ihm, Y.E., and Choo, W.K. 2002. Magnetic properties of epitaxially grown
11. xCoxO thin films by pulsed laser deposition, J. Appl. Phys., Cilt. 92, No. 10.1063/1.1513890 Zn1– 2, s. 6066-6071.
12. DOI: [10] Moreno, M.S., Kasama, T., Dunin- Borkowski,
13. Midgley, P.A., Steren, L.B., Duhalde, S., and Vignolo, M.F. 2006. Local study of the magnetism of Co- doped ZnO thin films, J. Phys. D: Appl. Phys., Cilt. 39, No. 9, s.1739- 1742. 3727/39/9/005 D., DOI:
14. 1088/0022- [11] Pan, F., Song, C., Liu, X.J., Yang, Y.C., and Zeng, F. Ferromagnetism and possible application in spintronics of
15. films, Mater. Sci. Eng., 2008, Cilt. ZnO s.1-35.
16. DOI: [12] Song, C., Pan, S.N., Liu, X.J., Li, X.W., Zeng, F., Yan, W.S., He, B., and Pan, F. 2007. Evidence of structural defect
17. temperature ferromagnetism in Co-doped ZnO, J. Phys.: Condens. Matter, Cilt. 19, No. 17, s.176229. DOI:10.1088/0953- 8984/19/17/176229 room- [13] Schmidt, H., Diaconu,
18. M., Hochmuth, H., Benndorf, G., Von Wenckstern, H., Biehn, G., Lorenz, M., and Grundmann, M. 2007. Electrical and optical spectroscopy on ZnO:Co films, Appl. Phys. A., Cilt. 88, No.
19. 1007/s00339-007-3992-y
20. DOI: [14] Bhatti, KP., Malik, V.K., and S. Chaudhary,
21. substituted ZnO thin films: a potential candidate for spintronics, J. Mater. Sci.: Mater. Electron., Cilt. 19 No. 8-9, s. 849-854. DOI: 10.1007/s10854-007-9501-4
22. Gungor, E., Gungor, T., Caliskan, D., Ceylan, A., and Ozbay, E. 2014. Co Doping Induced Structural and Optical
23. Prepared ZnO Thin Films, Applied Surface Science, Cilt. 318, s.309– 313.DOI:10.1016/j.apsusc.2014.06. 132 of
24. Sol-Gel [16] Saeki, H., Tabata, H., and Kawai, T. 2001.
25. properties of vanadium doped ZnO films, Solid State Commun. Cilt. 120, s. 439. DOI:10.1016/S0038- 1098(01)00400-8
26. electric [17] Han, S.J., and Song, J.W. 2002. A key to
27. ferromagnetism in Fe-doped ZnO: Cu, Appl. Phys. Lett., Cilt. 81, s.4212. DOI: 10.1063/1.1525885
28. Song, Y.Y., Park, K.S., Son, D.V., Yu, S.C., Kang, H.J., Shin, S.W., Whang, C.N., Lee, J.H., Song, J.H., and Lee, K.W. J. 2007. Korean Phys. Soc., Cilt. 50, s.1706.
29. Racheva, T.M., Critchlow, G.W. 1997. SnO2 thin films prepared by the sol-gel process, Thin Solid Films, Cilt. 292, s.299-302. DOI: 10.1016/S0040-6090(96)08956-0 [20] Ayoub, J.P., Favre, L., Ronda, A., Barbezier, I., Padova, P.D., Oliveri, B. 2006. Structural and magnetic properties
30. magnetic semiconductor, Materials Science
31. Processing, Cilt. 9, s.832-835. DOI:10.10106/j.mssp.2006.08.055 [21] Xu, W., Zhou, Y., Zhang, X., Chen, D., Xie, Y., Liu, T., Yan, W., Wei, S. 2007. Local structures of Mn in dilute magnetic semiconductor ZnMnO, Solid State Communications, Cilt. 141,
32. DOI:10.1016/j.ssc.2008.11.027
33. Quesada, A., Garcia, M.A., Crespo, P., Hernando, A. 2006. Materials for spintronic: ferromagnetism
34. interfaces, Journal of Magnetism and Magnetic Materials, Cilt. 304, s.75-78.
35. 1016/j.jmmm.2006.02.111
36. Ivill, M.. Pearton, S.J., Rawal, S., Leu, L., Sadik, P., Das, R., Hebard, A.F., Chisholm, M., Budai, J.D., Norton, D.P. 2008. Structure and magnetism of cobalt-doped ZnO thin films, New J. Phys. Cilt. 10, s. 065002. 2630/10/6/065002
37. Fitzgerald, C.B., Venkatesan, M., Lunney, J.G., Dorneles, L.S., Coey, J.M.D. 2005. Cobalt doped ZnO at room temperature dilute magnetic semiconductor, Appl. Surf. Sci. Cilt. 247,
38. DOI:10.1016/j.apsusc.2005.01.043 493–496. [25] Song, C., Zeng, F., Geng, K.W., Wang, X.B., Shen, Y.X., Pan, F. 2007. The magnetic properties of Co-doped ZnO diluted magnetic insulator films prepared by directcurrent reactive magnetron co-sputtering, J. Magn. Mater. Cilt. 309, s. 25–30. DOI:10.1016/j.jmmm.2006.06.012 [26] Swanepoel, R.
39. Determination of the thickness and optical constants of amorphous silicon, J. Phys., E. Sci. Instrum., Cilt. 16,
40. DOI:10.1088/00223735/16/12/02 3 [27] Güngör, T., Saka,
41. Calculation of the Optical Constants of a Thin Layer Upon a Transparent Substrate from the Reflection Spectrum
42. Algorithm, Thin Solid Films, Cilt. 467, 1016/j.tsf.2004.04.040 2004. Using a Genetic s. 319-325.
43. DOI: [28] Birgin, E.G., Chambouleyron, I., and Martinez, J.M. 1999. Estimation of optical constants of thin films using unconstraine optimization, Journal of Computational Physics, Cilt.
44. 1006/jcph.1999.6224 DOI: [29] Jurecka, S., Jureckova, 2003. Mullerova,
45. Algorithm approach to thin film optical parameters determination, Acta Phys Slovaca., Cilt. 53, s. 215- 221.
46. Genetic [30] Tauc, J., Grigorovici, R., Vancu, A. 1966. Optical properties and electronic structure of amorphous germanium, Phys. Stat. Sol., Cilt. 15,
47. Jin, Z., Murakami, M., Fukumura, T., Matsumoto,
48. Kawasaki, M., Koinuma, H. 2000. Combinatorial laser MBE synthesis of 3d ion doped epitaxial ZnO thin films, J. Crystal Growth, Cilt. 214- 215, s. 55-58. DOI: 10.1016/S0022- 0248(00)00058-0
49. A., [32] Yoo, Y.Z., Fukumura, T., Zhengwu, J., Hasegawa, K., Kawasaki, M., Ahmet, P., Chikyow, T., Koinuma, H. 2001. ZnO-CoO solid solution thin films, J. Appl. Phys, Cilt. 90, s. 4246-4250. 10.1063/1.1402142 DOI: