Tuning the electronic effective mass in double-dopedSrTiO3

We elucidate the relationship between effective mass and carrier concentration in an oxide semiconductor controlled by a double-doping mechanism. In this model oxide system, ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3\ensuremath{-}\ensuremath{\delta}}$, we can tune the effective mass ranging from 6 to $20{m}_{e}$ as a function of filling (carrier concentration) and the scattering mechanism, which are dependent on the chosen lanthanum- and oxygen-vacancy concentrations. The effective mass values were calculated from the Boltzmann transport equation using the measured transport properties of thin films of ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3\ensuremath{-}\ensuremath{\delta}}$. We show that the effective mass decreases with carrier concentration in this large-band-gap, low-mobility oxide, and this behavior is contrary to the traditional high-mobility, small-effective-mass semiconductors.