Structural and electronic properties of transparent conducting delafossite: a comparison between the AgBO2 and CuBO2 families (B = Al, Ga, In and Sc, Y)

The Ag-based delafossite transparent conducting oxides (TCO) are potential p-type materials for transparent electronics. However, they have attracted less attention compared with the Cu-based delafossite systems due to their difficult synthetic chemistry and relatively low conductivity. We present here a complete comparison of structural and electronic properties of these two families based on the results obtained from the periodic density functional calculation. The equilibrium structural parameters are obtained with the Perdew Burke Ernzerhof (PBE) exchange correlation functional in the calculation, while the electronic structure is investigated by using the screened hybrid functionals proposed by Heyd, Scuseria and Ernzerhof (HSE06). The structural stabilities of these two families of compounds are similar, being completely determined by the B-site metal ions. The density of states plots show that the valence band is relatively broader for the Ag-compounds. The Ag-4d orbitals are narrow and much lower in energy than the O p states. Therefore holes created at the oxygen site are highly localized and consequently have low mobility. The computed band gaps values are found to be in excellent agreement with the corresponding experimentally observed band gap values from optical measurements. The effective mass analysis suggests that for the Cu-compounds the conductivity follows the following trend: Sc > Ga ≈ Y > Al > In, in excellent agreement with the experimental observations. However, the calculated effective masses of the carriers suggest that the conductivity of the Ag-based compounds follows the following trend: Sc > Y > Ga > In > Al.