Influence of Oxygen on the Resistivity of Co‐Sputtered Transparent AZO Films

Abstract

In the present work co-sputtering from ceramic and metallic targets is used to reduce the oxygen content in aluminium doped zinc oxide. Films with thickness between 200 and 220 nm are sputtered at 100 and 250 C and investigated by X-ray diffraction, energy dispersive spectroscopy, and Hall measurements. It is found that reducing of the incorporated oxygen in the film leads to higher carrier concentration, mainly due to better effective activation of Al donors. Higher temperatures result in better carrier mobility due to improving the crystallinity. The best resistivity of 1.4 Â 10 À3 Ω cm of the highly transparent film prepared at 100 C is achieved. A larger oxygen reduction leads to lower resistivity, but also results in the significant deterioration of transmittances.

Possibilities of Increasing the Usability of Sputtered AZO Films as a Transparent Electrode

“…The XRD patterns show that the peak of the (002) line is shifted to the lower angles, which means higher interlayer distance in the c‐axis direction. The preferred orientation is also better and the surface morphologies exhibit well‐crystallized grains . From this data is clear that an excellent crystalline structure does not always mean the best electrical properties, which is in accordance with the results in Section 5.1.…”

“…Even the deposition of a ceramic target in an argon atmosphere may not be ideal. As shown, oxygen reduction would lead to better electrical properties and higher donor efficiency by co‐sputtering from metallic and ceramic targets . Assuming that Al occupies a substitution position, the oxygen concentration in the (ZnO/Al 2 O 3 ) target is slightly over‐stoichiometric.…”

“…Nomoto also reported that the higher degree of the preferential orientation limits the contribution of grain boundary scattering to carrier transport due to increasing carrier concentration and thus leads to the improving of the electrical conductivity . However, this relationship is not always valid as the reducing of the oxygen result in deterioration of preferential orientation and at the same time to improve electrical properties . The better preferred orientation can be caused by the external substrate heating or deposition on the buffer layer .…”

“…The possible reasons for the electrical deactivations of the dopant are the formation of dopant‐defect complexes, compensation of the electrons by acceptors (oxygen interstitials or zinc vacancy) and formation of secondary phases, for instance, Al 2 O 3 . Recently, it was shown that the concentration was increased by the preparation of the films under oxygen‐poor conditions . This influence can be explained by changing the zinc vacancy concentration, which is the dominant defect in oxygen‐rich conditions due to its low formation energy .…”

Improved sputtering method to deposit high conducting doped ZnO films without substrate heating

“…Some studies suggest that the properties of doped ZnO films can be enhanced with Zn supply during the co-deposition of ZnO and Zn. 20,21) However, the impact of Zn supply has not been clearly proven. Reports also indicate that post-deposition annealing under Zn-rich conditions can reduce resistivity.…”