Optical and Electrical Control of Confined Electrons in SrTiO₃/LaAlO₃ Quantum Well Heterostructures

While the SrTiO₃/LaAlO₃ (STO/LAO) system has been heavily studied in hopes of utilizing the interfacial 2DEG in all-oxide electronics, the 2.4 eV conduction band offset between STO and LAO also offers the opportunity to engineer quantum well (QW) heterostructures for use in electronic and optoelectronic devices. The operation of many such devices relies on the precise optical and/or electronic control of confined electrons through the stimulation of intersubband transitions or resonant tunneling. Here, we present optical spectroscopy measurements demonstrating room-temperature intersubband absorption in STO/LAO QW heterostructures on the order of hundreds of meV as well as tunneling measurements showing resonant tunneling through confined states. The presence of these phenomena indicates confinement of electrons in the STO conduction band and shows the ability to precisely control confined states in these structures. As a necessary prerequisite for the observation of these phenomena is the growth of high-quality samples, we also present a thorough structural characterization of our heterostructures indicating unprecedentedly low interfacial roughness of 0.3 unit cells/interface. We also discuss the feasibility of integrating these devices on Si (001) for use in Si photonics.