Understanding the role of Niobium, Molybdenum and Tungsten in realizing of the transparent n -type SnO 2 .

Based on the density functional theory, the defective band structures (DBSs), ionization energy and formation energy for Niobium (Nb), Molybdenum (Mo) and Tungsten (W)-doped SnO 2 are calculated. The DBSs show Nb, Mo and W substituting Sn (labeled as Nb Sn , Mo Sn and W Sn ) could form the localized impurity states which are above the conduction band minimum (CBM). These characteristics can be attributed to the energy of dopants' d-orbitals are much higher than that of Sn-s and -d orbital as well as O-2p orbitals, and the dopants with their neighboring atoms would form the non-bonding impurity states. The DBSs confirm Nb Sn , Mo Sn and W Sn are typical n -type defects in SnO 2 . The ionization energies ϵ (0/+) for Nb Sn , Mo Sn and W Sn are higher than 0.22 eV above CBM, indicating these defects could be fully ionized. We find the NbO and MoO 3 are promising dopant sources, as the thermodynamic equilibrium fabrication scheme is considered. Taking Nb-doped SnO 2 as an example, we find a few Nb Sn could induce high conductivity (541 S cm -1 ). These results suggest that SnO 2 containing Nb Sn , Mo Sn and W Sn are promising n -type semiconductors. Our findings would provide a better understanding of the n -type properties in Nb, Mo and W-doped SnO 2 .