A new approach in layer-by-layer growth of oxide materials by pulsed laser deposition

Abstract

Pulsed laser deposition (PLD) has become thin film deposition technique with increasing prominence. One of the advantages above other techniques is the possibility to growth at relative high background pressures, with a large freedom in choosing the kind of gas. An example is oxygen in the case of high Tc superconductors and giant magnetic resistors. However, the advantage of relative high pressures hinders the use of a number of diagnostics and monitor techniques, like reflective high energy electron diffraction (RHEED). With the introduction of the possibility to use RHEED at standard PLD pressures, it became possible to study the growth of oxide materials under different oxygen and temperature conditions. In this paper we employed this technique on SrTiO3, which can be grown in different growth modes depending on growth temperature and oxygen pressure during deposition. Applying a modified etch treatment on SrTiO3 single crystals, a real 2D growth mode could be observed by the homo-epitaxial growth of SrTiO3, as indicated by RHEED oscillations. In addition to the RHEED oscillations another phenomenon is observed, typical for PLD. The pulsed way of deposition leads to discontinuities in the intensity of the diffracted pattern. This is caused by the mobility of the deposited material from a disordered distribution till an ordered one and leads to a characteristic exponential slope with characteristic relaxation time constants. These time constants give extra information about relaxation, crystallization, and nucleation of the deposited material during growth. Finally, a new approach to deposit these complex oxide materials will be introduced. This, so-called interval deposition, is based upon the results obtained from the intensity oscillations as well as relaxations. The basic idea is to deposit an equivalent of one unit cell of material in such a short time that no coalescence in larger islands can occur, followed by a relaxation time before the next unit cell layer is deposited. This interval deposition leads to an imposed layer by layer growth.