Atomically Flat SrRuO$_{3}$ Conductive Thin Films on SrTiO$_{3}$ (001) by Pulsed Laser Deposition

Atomically flat surfaces are important for thin film multilayers, superlattices, and heterostructures. For SrRuO$_{3}$ thin films grown on perovskite substrates, higher oxygen pressure is commonly used to achieve desired stoichiometry, crystallinity and conductivity, but it can also cause step bunching, pin holes and finger-like structures which destroy film/substrate coherency. We have found the finger-like structure is due to the slow 3-layer-nucleation process that occurs on the TiO$_{2}$ terminated SrTiO$_{3 }$substrate, whereas step bunching is due to excessive step mobility. Using a transition layer on SrTiO$_{3}$ that establishes the SrO termination, and adjusting deposition parameters and step spacing that reduce step migration time, we have obtained atomically flat SrRuO$_{3}$ films free of the above morphological defects. These films show a large enhancement of electrical conductivity, making them suitable for various applications.