Study of oxygen diffusion process in BaSnO3 and SrTiO3 films

BaSnO3 has not only been recognized for its superb semiconducting properties, such as its high electron mobility when doped with La, but also for its excellent oxygen stability even at high temperatures. However, previous experiments on the oxygen stability of BaSnO3 films grown on SrTiO3 substrates have been plagued by the increased conductivity of SrTiO3 at high temperatures. In order to remove this problem, we have studied undoped and 1 % La-doped BaSnO3 films grown on MgO substrates, which do not exhibit change in conductivity at high temperatures. The resistance of the films was measured using four-point gold wire contacts, at various temperatures ranging from 500°C to 750°C, while switching the background atmosphere between oxygen and argon to induce oxygen diffusion. The results were used to calculate the oxygen diffusion constant of the BaSnO3 film. As a comparison we have also measured a SrTiO3 film grown on a MgO substrate, which showed quicker change of resistance than the BaSnO3 film. At the same time we observed that the resistance of the SrTiO3 film at high temperatures is higher than that of the BaSnO3 film, which can be attributed to the low mobility of carriers in SrTiO3.