Theory of Defects in n-Type Transparent Conducting Oxides

A range of computational modelling techniques are employed to explore the structures, defect and electronic properties of three transparent conducting oxides (TCOs): SnO₂, In₂O₃ and ZnO. Bulk interatomic potential (IP) based calculations are carried out to model point defects in SnO₂ and In₂O₃. We report new IPs for the two binary oxides, which offer an improvement over the previously available models, and give defect formation energies comparable with those obtained using density functional theory (DFT). The intrinsic point defects in ZnO are investigated in detail using a hybrid quantum mechanical/molecular mechanical (QM/MM) embedded cluster approach. The formation energies show the oxygen vacancy to be the most favourable under O-poor conditions and zinc vacancies under O-rich conditions. Our calculations are also able to assign several of the widely studied luminescence bands to defect states. For extrinsic dopants, including in ZnO, we compute the structure and formation energies of Li and H dopants in both substitutional and interstitial form and their complexes, the Li_{Zn}-Lii_{(oct)} complex has the lowest formation energy in Zn-poor conditions. The HO is energetically favoured compared to Hi. Using QM/MM calculations, we investigate the native point defect on the electrical and optical properties of In₂O₃. The oxygen vacancy is the lowestenergy donor defect, with a predicted luminescence peak at 2.12 eV using the B97-2 functional. Finally, we study the solid-solution of In₂O₃ and SnO₂ over a range of dopant concentrations, which provide local structure information.