  The two-dimensional electron gas at the surface of titanates gathered
attention due to its potential to replace conventional silicon based
semiconductors in the future. In this study, we investigated films of the
parent perovskite CaTiO$_3$, grown by pulsed laser deposition, by means of
angular-resolved photoelectron spectroscopy. The films show a c(4x2) surface
reconstruction after the growth that is reduced to a p(2x2) reconstruction
under UV-light. At the CaTiO$_3$ film surface, a two-dimensional electron gas
(2DEG) is found with an occupied band width of 400 meV. With our findings
CaTiO$_3$ is added to the group of oxides with a 2DEG at their surface. Our
study widens the phase space to investigate strontium and barium doped
CaTiO$_3$ and the interplay of ferroelectric properties with the 2DEG at oxide
surfaces. This could open up new paths to tailor two-dimensional transport
properties of these systems towards possible applications.
