  SrVO3 and SrNbO3 are perovskite-type transition-metal oxides with the same d1
electronic configuration. Although SrNbO3 (4d1) has a larger d orbital than
SrVO3 (3d1), the reported electrical resistivity of SrNbO3 is much higher than
that of SrVO3, probably owing to nonstoichiometry. In this paper, we grew
epitaxial, high-conductivity stoichiometric SrNbO3 using pulsed laser
deposition. The growth temperature strongly affected the Sr/Nb ratio and the
oxygen content of the films, and we obtained stoichiometric SrNbO3 at a very
narrow temperature window around 630 ${\deg}$C. The stoichiometric SrNbO3
epitaxial thin films grew coherently on KTaO3 (001) substrates with high
crystallinity. The room-temperature resistivity of the stoichiometric film was
$2.82 {\times} 10^{-5} {\Omega}$cm, one order of magnitude lower than the
lowest reported value of SrNbO3 and comparable with that of SrVO3. We observed
a T-square dependence of resistivity below $T^{\ast}$ = 180 K and non-Drude
behavior in near-infrared absorption spectroscopy, attributable to the
Fermi-liquid nature caused by electron correlation. Analysis of the T-square
coefficient A of resistivity experimentally revealed that the 4d orbital of Nb
that is larger than the 3d ones certainly contributes to the high electrical
conduction of SrNbO3.
