Rewritable nanoscale oxide photodetector

Nanophotonic devices seek to generate, guide, and/or detect light using structures whose nanoscale dimensions are closely tied to their functionality.1,2 Semiconducting nanowires, grown with tailored optoelectronic properties, have been successfully placed into devices for a variety of applications.3–5 However, the integration of photonic nanostructures with electronic circuitry has always been one of the most challenging aspects of device development. Here we report the development of rewritable nanoscale photodetectors created at the interface between LaAlO3 and SrTiO3. Nanowire junctions with characteristic dimensions 2-3 nm are created using a reversible AFM writing technique.6,7 These nanoscale devices exhibit a remarkably high gain for their size, in part because of the large electric fields produced in the gap region. The photoconductive response is gate-tunable and spans the visible-to-near-infrared regime. The ability to integrate rewritable nanoscale photodetectors with nanowires and transistors in a single materials platform foreshadows new families of integrated optoelectronic devices and applications. The discovery of a quasi two-dimensional electron gas (q2DEG) at the interface between insulating oxides8 has accelerated interest in oxide-based electronics.9 The interface between LaAlO3 and SrTiO3 undergoes an abrupt insulatorto-metal transition as a function of the number of LaAlO3 layers;10 for structures at or near the critical thickness (dc = 3 unit cells), the conductance becomes highly sensitive to applied electric fields.10 By applying the electric field locally using a conducting AFM probe, one can control this metal-insulator transition with resolution approaching one nanometer.6,7 Devices such as rectifying junctions11 and transistors7 can be created, modified, and erased with extreme nanoscale precision. Additionally, as LaAlO3 and SrTiO3 are both wide-bandgap insulators they are essentially transparent at visible wavelengths, making it an interesting material system on which to search for photonic functionality. In this letter we demonstrate the creation of nanophotonic devices at the LaAlO3/SrTiO3 interface using conductingAFM lithography (Figure 1a). Oxide heterostructures, consisting of 3 units cells of LaAlO3 on TiO2-terminated SrTiO3 (ref. 12), are grown by pulsed-laser deposition (see the Supplementary Information for details about growth conditions). Following contact to the interface with low-resistance Au electrodes, nanostructures are created at the LaAlO3/SrTiO3 interface by applying positive voltages to a conducting AFM tip. Nanoscale insulating gaps are formed by “cutting” these nanowires with a negatively-biased AFM tip that passes over the nanowire. Electronic nanostructures can be created with a a