Electrical and Optical Properties of Nb-doped SrSnO3 Epitaxial Films Deposited by Pulsed Laser Deposition

Nb-doped SrSnO3 (SSNO) thin films were epitaxially grown on LaAlO3(001) single-crystal substrates using pulsed laser deposition under various oxygen pressures and substrate temperatures. The crystalline structure, electrical, and optical properties of the films were investigated in detail. X-ray diffraction results show that the cell volume of the films reduces gradually with increasing oxygen pressure while preserving the epitaxial characteristic. X-ray photoelectron spectroscopy analysis confirms the Nb5+ oxidation state in the SSNO films. Hall-effect measurements were performed and the film prepared at 0.2Pa with the 780 degrees C substrate temperature exhibits the lowest room-temperature resistivity of 31.3 m Omega cm and Hall mobility of 3.31cm(2)/Vs with a carrier concentration at 6.03 x 10(19)/cm(3). Temperature-dependent resistivity of this sample displays metal-semiconductor transition and is explained mainly by electron-electron effects. Optical transparency of the films is more than 70% in the wavelength range from 600 to 1800nm. The band gaps increase from 4.35 to 4.90eV for the indirect gap and 4.82 to 5.29eV for the direct by lowering oxygen pressure from 20 to 1 x 10(-3)Pa, which can be interpreted by Burstein-Moss effect and oxygen vacancies generated in the high vacuum.