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 sub(2)O sub(3) using density functional theory. The surface energies follow the order gamma (100) gamma 7(110) > gamma (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, SnO sub(2) 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 In sub(2)O sub(3) conduction states; the enthalpy of solution is estimated to be 60 kJ mol super(-1).