Structure, stability and work functions of the low index surfaces of pure indium oxide and Sn-doped indium oxide (ITO) from density functional theory

Indium sesquioxide is a transparent conducting oxide material widely used in photovoltaic and solid-state lighting devices. We report a study of the surface properties of the thermodynamically stable bixbyite phase of In ₂O₃ using density functional theory. The surface energies follow the order γ(100) > γ(110) > γ(111), with the charge neutral (111) termination being the lowest energy cleavage plane. The surface work functions (vertical ionisation potentials) are calculated using a non-local hybrid density functional, and show good agreement with recent experimental measurements. Finally, SnO₂ doping of the (111) surface is presented, where the Sn substitutions are more favourable on the surface sites and the excess electrons are delocalised amongst the In₂O ₃ conduction states; the enthalpy of solution is estimated to be 60 kJ mol^-1.