By inserting a SrZrO 3 buffer layer between the film and the substrate, we demonstrate a significant reduction of the threading dislocation density with an associated improvement of the electron mobility in La:BaSnO 3 films. A room temperature mobility of 140 cm 2 V −1 s −1 is achieved for 25-nm-thick films without any postgrowth treatment. The density of threading dislocations is only 4.9 × 10 9 cm −2 for buffered films prepared on (110) TbScO 3 substrates by pulsed laser deposition.Transparent conducting oxides (TCOs) have attracted attention due to their unique properties and applications in electronic devices such as transparent displays and transistors. 1,2 Recently, the transparent perovskite La:BaSnO 3 has gained interest as a novel TCO due to its high mobility at room temperature (RT). 3,4 Single crystals of La:BaSnO 3 have been reported to have RT mobilities as high as 320 cm 2 V −1 s −1 (mobile carrier concentration n = 8 × 10 19 cm −3 ). 4 At doping concentrations above 10 19 cm −3 , La:BaSnO 3 has the second highest RT electron mobility among TCOs and other oxide single crystals 4-6 , exceeded only by CdO. 7 The high RT mobility in La:BaSnO 3 has been attributed to the small electron-phonon interaction and small electron effective mass (m * e = 0.19 m 0 ) arising from the large dispersion of the conduction band comprised of Sn 5s orbitals. 8-10 However, to fully explore the potential of La:BaSnO 3 , thin films with high mobilities are also required.Recently, several efforts to achieve high carrier mobility in La:BaSnO 3 films have been reported. 11-18 Nevertheless, as compared to bulk single crystals, even the best La:BaSnO 3 epitaxial films show a reduced mobility (≤ 183 cm 2 V −1 s −1 ), 18 which specifically has been attributed to scattering from charge defects, such as threading dislocations (TDs) 8,18-20 and, more generally, to small carrier relaxation times. 8,9 TDs form for a large lattice mismatch between film and substrate, and extend perpendicularly through the films. The obvious solution to reduce TDs in La:BaSnO 3 films is to use latticematched substrates, but unfortunately none exists. The substrate with the closest lattice match that is commercially available is PrScO 3 , mismatched by −2.3%. 21 With such a high mismatch only thin commensurate layers of BaSnO 3 can be grown; at a thickness of 32 nm the reported BaSnO 3 films are almost fully relaxed and contain high densities of TDs. 19 To reduce the dislocation density in the La:BaSnO 3 film, we explored the insertion of an undoped BaSnO 3 a) Corresponding author: p.ngabonziza@fkf.mpg.de buffer layer at the interface between the substrate (TbScO 3 ) and the La:BaSnO 3 film. As the thickness of the BaSnO 3 layer increases, the TD density decreases as the threading component of dislocations annihilate each other, leaving behind a network of misfit dislocations. This method is known and has already led to the highest mobilities in BaSnO 3 films to date; but even for thick buffer layers (330 nm), the remaining TD density is still 1.2 × 10 1...

The authors analyze the x-ray photoelectron spectra of SrTiO3(100) (STO) substrates to clarify the electronic structure characteristics induced by a sputter–anneal procedure. The survey spectra, the valence band spectra, and the relevant core level spectra, i.e., Sr 3s, Sr 3p, Sr 3d, Sr 4s, Sr 4p, Ti 2p, Ti 3s, Ti 3p, O 1s, and O 2s along with their satellite structures, of both pristine and sputtered and annealed STO have been measured. A comparison of spectra reveals the appearance of new features in the Ti 2p spectra of sputtered and annealed STO, corresponding to Ti3+ states and gap states near the Fermi energy. The presence of Ti3+ states points to the formation of a two-dimensional electron system at the STO surface generated by Ar+ sputtering and annealing in vacuum. Furthermore, the sputter-annealed surface shows only minor carbon contamination as compared to that of the pristine substrate.

For La-doped BaSnO3 thin films grown by pulsed laser deposition, we combine chemical surface characterization and electronic transport studies to probe the evolution of electronic states in the band structure for different La-doping contents. Systematic analyses of spectroscopic data based on fitting the core electron line shapes help to unravel the composition of the surface as well as the dynamics associated with increasing doping. These dynamics are observed with a more pronounced signature in the Sn 3d core level, which exhibits an increasing asymmetry to the high binding energy side of the peak with increasing electron density. The present results expand the current understanding of the interplay between the doping concentration, electronic band structure, and transport properties of epitaxial La:BaSnO3 films.