Influence of cation off-stoichiometry on structural and transport properties of (Ba,La)SnO3 epitaxial thin films grown by pulsed laser deposition.

We investigate the influences of cation off-stoichiometry on structural and transport properties of 3% La-doped BaSnO3 (BLSO) epitaxial thin films grown on SrTiO3 substrates by pulsed laser deposition. We show that cation off-stoichiometry, namely, Sn excess and Sn deficiency, is introduced by variations in either laser fluence or the cation composition of the target used for the film growth and that the cation off-stoichiometry influences the properties of the grown films. While all films investigated in this study undergo relaxations from the substrate-induced strain, the out-of-plane lattice constant decreases with the increase in the Sn content in the film. The electrical conductivity, carrier concentration, and mobility are strongly dependent on the type of the cation off-stoichiometry (Sn excess and Sn deficiency). The highest room-temperature mobility, 35 cm2/ V-1s-1, is seen for a film grown by ablating the stoichiometric target with a fluence of 1.6 J/cm2, which keeps the cation ratio in the film close to the stoichiometric one. The conductivity and the carrier concentration of the Sn-excess films grown with the fluence smaller than 1.6 J/cm2 are as high as 2 х 103 S/cm and 5 х 1020 cm-3, respectively, while the mobility remains as low as 25 cm2/V-1s-1. The observed carrier concentration is slightly higher than that calculated from the stoichiometric composition of BLSO, implying that the excess Sn in the films provides additional carriers and also acts as scattering centers for the carriers. On the other hand, no measurable electrical conduction is observed in the Sn-deficient films grown with a fluence greater than 1.6 J/cm2, indicating that the carriers provided by the dopants are trapped by defects due to the Sn deficiency. We also show that cation off-stoichiometry influences the surface morphology of the films. Our results highlight that the cation stoichiometry of the BLSO films is an important factor influencing their properties. [ABSTRACT FROM AUTHOR]