Abstract
We propose an explanation for the origin of n-type electrical conductivity in SnO2 based on the results obtained from the DFT+U simulations. Two competitive intrinsic point defects, namely oxygen vacancy and hydrogen impurity, have been considered at different positions within the crystalline lattice in order to find out the equilibrium configurations and to analyze corresponding density of states (DOS) patterns along with the electron localization function (ELF). It has been demonstrated that hydrogen could be solely responsible for the n-type conductivity whereas the oxygen vacancy appears to have not a notable influence upon it. The computational analysis is backed up by some experimental data for undoped tin dioxide.
Highlights
Tin dioxide (SnO2) is an intrinsic n-type wide-band gap (3.6 eV at room temperature) oxide semiconductor.[1,2,3,4] Properties, such as high electrical conductivity and optical transparency in the visible region together with the excellent chemical and mechanical stability, make the SnO2 to be a perfect replacement for tin-doped indium oxide (In2O3), which is the industry standard for transparent conductive oxide (TCO) materials.[4]Since 1907, when the first TCO was reported by Badeker,[5] large and decisive improvements have been done for the n-type part of the field to such an extent that its zenith has been nearly reached.[1]
Our research is based on the density functional theory (DFT) within the generalized gradient approximation (GGA) as it is implemented in the Vienna ab initio simulation package (VASP).[9]
Valence electronic states are expanded in a set of periodic plane waves, and the interaction between the core electrons and the valence electrons is treated through the projector augmented wave (PAW) pseudo-potential method proposed by Bloch[10] and adapted by Kresse and Joubert.[11]
Summary
Since 1907, when the first TCO was reported by Badeker,[5] large and decisive improvements have been done for the n-type part of the field to such an extent that its zenith has been nearly reached.[1] in spite of more than 100 years of investigation, the origin of the n-type conductivity in SnO2 is still under discussion.[6,7,8] The intrinsic ability of this material to conduct electrons has been often attributed to the presence of unintentionally created donor centers, usually identified as metallic interstitials or oxygen vacancies that produce shallow donor states near the conduction band (CB) edge.[4,7,9,10] Singh et al.[8] recently have put forward the idea of hydrogen atom in order to explain the presence of n-type carriers in SnO2. Negative charge on hydrogen in case of the VO configuration can be explained by the F center presence at the oxygen vacancy site
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