On the Possibility of p-type Doping in Barium Stannate

The combination of optical transparency and bipolar dopability in a single material would revolutionise modern opto-electronics. Of the materials known to be both p- and n-type dopable (such as \ce{SnO} and \ce{CuInO2}), none can satisfy the requirements for both p- and n-type transparent conducting applications. In the present work, perovskite \ce{BaSnO3} is investigated as a candidate material: its n-type properties are well characterised, with La-doping yielding degenerate conductivity and record electron mobility, while it has been suggested on a handful of occasions to be p-type dopable. Herein, group 1 metals Li, Na and K and group 13 metals Al, Ga and In are assessed as p-type acceptor defects in \ce{BaSnO3} using hybrid density functional theory. It is found that while K and In can induce hole concentrations up to \SI{e16}{\per\centi\meter\cubed}, the low energy oxygen vacancy pins the Fermi level in the band gap and ultimately prevents metallic p-type conductivity being achieved in \ce{BaSnO3}. Nevertheless, the predicted hole concentrations exceed experimentally reported values for K-doped \ce{BaSnO3}, suggesting that the performance of a transparent p-n homo-junction made from this material could be significantly improved.