Perovskite oxide SrSnO3 has attracted considerable attentions recently due to its high carrier mobility and high transparency. Here, we experimentally and theoretically investigated the effects of La and Pb doping on the microstructure, band gaps, and electrical properties of SrSnO3 epitaxial thin films. X-ray diffraction analysis showed that the in-plane lattice constants of Pb-doped SrSnO3 (SrSn1-xPbxO3, x = 0-1, SSPO) films increased from 4.053 to 4.178 Å with the increase in Pb doping content. High-resolution transmission electron microscopy images revealed that SSPO films were coherently grown on LaAlO3(001) substrates. The optical band-gap values were considerably decreased gradually from 4.43 to 2.16 eV with Pb doping content while maintaining high optical transmittance in the visible wavelength range. Density functional theory calculations showed that the narrowing of band gap was attributed to a finite overlap between Pb 6s and Sn 5s orbitals around the bottom of the conduction band. As doping with 5% La in SSPO films, the electrical conductivity was improved greatly, and transport properties were investigated through temperature-dependent resistivity and Hall measurements. A lowest room-temperature resistivity of 0.5 mΩ cm and a maximum mobility of 39.9 cm2/Vs were observed in 5% La in the SSPO film at x = 1. Such wide-range tuning of the band gaps and excellent electrical properties of La- and Pb-doped SrSnO3 epitaxial thin films may provide promising applications in optoelectronic devices.
Keywords: DFT calculations; SrSnO; band gap; pulsed laser deposition; thin films; transport properties.