Studies of LaAlO 3“100” surfaces using RHEED and REM. I: twins, steps and dislocations

Abstract

Lanthanum-aluminate (LaAlO 3) is one of the optimum substrates for epitaxial growth of YBa 2Cu 3O 7 − x thin films. In this paper, the structures of the “100” surfaces of annealed LaAlO 3 are studied using reflection electron microscopy (REM). The importance of substrate steps on the growth of defects in the film is shown. It has been found that a “010” twin boundary is normally terminated with a 〈001〉 step at the surface. Dislocations are not observed in the flat surface areas but occur at the twin boundaries that intersects the “100” surface. The observed dislocation is screw-type with Burgers vector a〈100〉. Numerous [010] and [001] “sawtooth” steps have been observed, and they are believed to be the lowest surface energy steps. It is suggested that the “100” surfaces are terminated entirely with either the LaO layer or the AlO layer, but not a mixture of both. The miscut angle and the heights of surface steps are measured using the mirror imaging technique. Finally, the effect of surface contaminants on the growth of surface steps is shown, and a growth mechanism is proposed.