Sequential imposed layer epitaxy of cuprate films

Abstract

Layer-by-layer epitaxy has been used to grow cuprate films since the discovery of high-Tc compounds. This deposition technique is in principle suitable for the growth of layered crystalline structures. However, the sequential deposition of atomic layer by atomic layer of cuprate compounds has presently not been optimized. Among the difficulties to overcome are the need to control separately the deposition of three to five elements, the oxidation requirements, and the observed tendency toward the nucleation of three-dimensional aggregates. Nevertheless, this deposition process is the only one which allows one to build artificial cell structures such as Bi2Sr2Ca(n−1)CunOy withn as large as 10. This process will also be the best one to grow films of the so-called infinite layer phase compounds belonging to the Sr1−xCaxCuO2 family, in order to improve the transport properties and the morphological properties of the cuprate films. When performed at high substrate temperature (typically more than 600°C), the layer-by-layer epitaxy of cuprates exhibits usually 3D aggregate nucleation. Then the growth of the film no longer obeys the layer-by-layer sequence imposed during the deposition. We present here two experimental situations of true 2D sequential imposed layer epitaxy: the growth at 500°C under atomic oxygen pressure of Bi2Sr2CuO6 and of Sr1−xCaxCuO2 phases.