  Oxide two-dimensional electron gases (2DEGs) promise high charge carrier
concentrations and low-loss electronic transport in semiconductors such as
BaSnO$_{3}$ (BSO). ACBN0 computations for BSO/SrNbO$_{3}$ (SNO) interfaces show
Nb-4$\textit{d}$ electron injection into extended Sn-5$\textit{s}$ electronic
states. The conduction band minimum consists of Sn-5$\textit{s}$ states ~1.2 eV
below the Fermi level for intermediate thickness 6-unit cell BSO/6-unit cell
SNO superlattices, corresponding to an electron density in BSO of ~10$^{21}$
cm$^{-3}$. Experimental studies of analogous SNO/BSO interfaces grown by
molecular beam epitaxy confirm significant charge transfer from SNO to BSO.
$\textit {In situ}$ angle-resolved X-ray photoelectron spectroscopy studies
show an electron density of ~4 $\times$ 10$^{21}$ cm$^{-3}$. The consistency of
theory and experiment shows that BSO/SNO interfaces provide a novel materials
platform for low loss electron transport in 2DEGs.
