Fabrication of SrTiO₃ field effect transistors with SrTiO _3-δ source and drain electrodes

We have developed a process for fabricating top-gate SrTiO₃ field-effect transistors (FETs) where the critical channel interface is constructed before forming the source and drain electrodes in order to reduce the density of defects in the transistor channel. Metallic source and drain electrodes are formed by Argon ion milling, which is an efficient way of introducing oxygen vacancies into a thin surface layer of SrTiO₃. These vacancies function as donors, inducing metallic conductivity in the electrode regions. This technique can be used to obtain clean interfaces, suppress the formation of lattice imperfections, and avoid impurities in the FET channel because the electronically active interface is constructed at an early step of the device fabrication process. Metallic conductivity of the SrTiO _3-δ source and drain electrodes was maintained even after annealing the device at up to 600°C. Contact with the transistor channel remained ohmic at least down to 50 K.