Optical properties of La-based high-$K$ dielectric films

We have characterized thin films of $LaScO3$ and $LaAlO3$ which were grown by molecular beam deposition on Si substrates. Samples of $LaScO3$ were also grown by pulsed laser deposition on MgO substrates. Using transmission studies between 1.5 and $6eV$⁠, we have established that low temperature deposition leads to a reduced band gap with respect to the bulk crystal. Furthermore, using spectroscopic ellipsometry from $5to9eV$ we observe substantial differences in near-band gap absorption between thin and thicker films for both materials. We obtain a band gap of $5.84eV$ for the thinner film of $LaAlO3$⁠, whereas we find a band gap of $6.33eV$ for the thicker film of $LaAlO3$⁠. Similarly we find band gaps of 5.5 and $5.96eV$⁠, respectively, for thin and thick films of $LaScO3$⁠.