Abstract
Highly conductive TiO2 films with different Nb doping levels (up to 5 at%) were prepared by reactive DC magnetron sputtering under precise control of the oxygen partial pressure. They were deposited on unheated substrates, covered with a protective Si3N4 layer, and subsequently annealed at 300 °C. The doping efficiency of Nb is greater than 90%. Conductivity is a maximum for a partly oxidized target in the transition range. The best films exhibit a resistivity of 630 µΩ cm and a mobility of 7.6 cm2/Vs combined with a high transparency above 70%. Comparing the behavior of undoped and Nb-containing films, intrinsic limits of the conductivity in the TiO2−x:Nb system could be observed, and a consistent model explaining these findings is presented. The conductivity is limited—by decreasing electron density due to Nb oxidation—by increasing incorporation formation of Nb2O5 clusters as scattering centers with increasing oxygen partial pressure and Nb concentration, by a transition from the crystalline to the amorphous state of the films below a critical oxygen partial pressure.
Highlights
Modern displays, solar cells, and other applications need layers as front electrodes that are both conductive and transparent [1,2,3]
In 2005, TiO2−x films doped with Nb were reported to fulfill the requirements of high transparency and conductivity [5]
Electronic transport arises from highly-oriented d-orbitals [6], which are less likely to overlap, so that high electron mobilities are not expected. We discussed this issue and the criteria necessary to realize metallic conductivity [7]. There, it was demonstrated how both metallike conductivity and high transparency can be achieved in undoped TiO2−x and why the conductivity values and temperature behavior reported in the literature vary so much
Summary
Solar cells, and other applications need layers as front electrodes that are both conductive and transparent [1,2,3]. The materials of choice are currently oxides of metals such as Ga, In, Cd, Sn, and Zn, so-called transparent conducting oxides (TCOs) [4] They all have in common the fact that their conduction band is built from empty s-orbitals, enabling high electron mobilities. In 2005, TiO2−x films doped with Nb were reported to fulfill the requirements of high transparency and conductivity [5] In these materials, electronic transport arises from highly-oriented d-orbitals [6], which are less likely to overlap, so that high electron mobilities are not expected. We discussed this issue and the criteria necessary to realize metallic conductivity [7] There, it was demonstrated how both metallike conductivity and high transparency can be achieved in undoped TiO2−x and why the conductivity values and temperature behavior reported in the literature vary so much
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
