| Thin film crystalline oxides exhibit a wide variety of interesting physical phenomena, including superconductivity and switchable magnetism. One material of interest in the complex oxide community is the RTiO 3/SrTiO3 (RTO/STO) system, where R is a trivalent rare-earth element such as La (LTO) or Gd (GTO). It was discovered that a 2-dimensional electron gas (2DEG) forms at the interface of these otherwise insulating oxides, supporting a carrier concentration of ~3 x 1014 cm-2. This charge density is an order of magnitude higher than what is achievable in state-of-the-art III-N semiconductor systems, but devices made with these oxides tend to have poor electron mobility at room temperature.;We demonstrate an approach toward realizing high mobility and high carrier concentration devices by the epitaxial integration of single crystalline LTO/STO and GTO/STO structures onto silicon by molecular beam epitaxy. The effect of doping the STO films with La to realize a high carrier concentration is also studied, and electrical characterization shows that high 2DEG densities are found in each system.;One challenge to achieving high mobility is an unfavorable band alignment between STO and Si, which we show by x-ray photoemission spectroscopy to be a staggered (type II) gap. The Si conduction band is positioned ~0.7 eV higher than the STO conduction band and thus confines the electrons to the low mobility oxide. We demonstrate that by increasing the oxygen content at the interface, the conduction band offset can be reduced to nearly zero, improving the number of carriers in the silicon, which we quantify with a dual channel conduction model. This approach provides a route toward remotely doping semiconductors by band offset engineering and also serves as an example of combining multifunctional complex oxides with conventional semiconductor technology. |
