Combinatorial study of Nb doped ZnO
J. N. Swallow
1,*
, S. Sathasivam
2
, B. A. D. Williamson
2
, R. E. Treharne
1
,
C. J. Carmalt
2
, I. P. Parkin
2
, V. R. Dhanak
1
, D. O. Scanlon
2
, T. D. Veal
1
,
1
Stephenson Institute for Renewable Energy and Department of Physics, University of
Liverpool, Liverpool UK
2
Department of Chemistry, University College London, London, UK
*Corresponding email
Traditionally dopants for TCOs have been chosen by selecting elements one to the right in
the periodic table of the host elements; for example F to substitute O in SnO
2
:F and Al to
substitute Zn in ZnO:Al. While there have been some suggestions of methodologies for
determining whether cation or anion doping is preferable for particular materials [1], further
improvements seem unlikely using this doping approach. However, there is increasing
evidence that non-conventional choices of dopants may offer improved performance in terms
of enhanced transparency, conductivity and carrier mobility. For example, there are several
reports of Mo doped In
2
O
3
having better properties than Sn doped In
2
O
3
[2].
It is within this context that here a combinatorial chemical vapour deposition method
is used to investigate Nb doping of ZnO. This methodology enables a wide range of doping
levels to be characterized rapidly within one sample. Mapping transmission, four point probe,
x-ray diffraction and x-ray photoemission spectroscopy (XPS) measurements are used to
determine transparency and conductivity as a function of Nb content. Hall effect is
additionally used to determine the corresponding carrier concentration and mobility values.
Hybrid functional density functional theory calculations are used to calculate the band
structure of Nb doped ZnO. DFT findings are compared with the XPS results. Comparisons
are made with previous results on other ZnO dopants.
[1] C. Li, J. Li, S.-S. Li, J.-B. Xia and S.-H. Wei, Appl. Phys. Lett.
100
(2012) 262109.
[2] D. S. Bhachu, D. O. Scanlon, T. D. Veal, I. Parkin,
et al.
Chem. Mat.
27
(2015) 2788.
PS2 1
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