Improved stoichiometry and misfit control in perovskite thin film formation at a critical fluence by pulsed laser deposition

Abstract

Pulsed laser deposition (PLD) is a good method for growing high-quality functional oxide thin films because of the technical simplicity and the ease with which deposition can be switched from one material to another. However, the repeatability of film quality is often hard to achieve, especially when using several different PLD systems. Here we report the steps that we have taken to grow nearly bulk-equivalent defect-free thin films, with SrTiO3 as an example, by using PLD in a reproducible fashion. The ablation laser fluence was found to have a very strong effect on the lattice constant and defect structure of the films. Nonstoichiometric transfer of material from the ablation target was observed when either the laser fluence or the beam spot area was inadequate.

Electronic Reconstruction at the Interface Between Band Insulating Oxides: The LaAlO3/SrTiO3 System

“…PLD growth is very easy and allows, in principle, a quasi-stoichiometric transfer of the target composition to the substrate. On the other hand, it has been shown that even in the case of STO homoepitaxy, the overall stoichiometry, thus the defect density, of PLD grown films is extremely sensitive to the deposition conditions, in particular to the target to substrate distance, oxygen background pressure, heater temperature, laser fluence and laser spot areas [34]. In short, the stoichiometric transfer of ablated species to the substrate depends crucially on the plume dynamics.…”

Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

“…[16] However, at less than optimal growth conditions, the highly energetic plume-substrate interactions can produce undesirable departures from stoichiometry. [17,18] As summarized in Table 1 of Supporting Information, the PLD growth conditions used in published reports on the LAO/STO interface formation were not uniform, suggesting that the differences in the growth parameters might contribute to inconsistent observations and/or interpretations of interface conductivity. Most importantly, compared to conventional PLD growth conditions for typical perovskite oxides, [19,20] many LAO/STO heterostructures were grown at unusually low P(O 2 ) and rather high temperatures.…”

Pulsed laser ablation of complex oxides: The role of congruent ablation and preferential scattering for the film stoichiometry

“…In particular, STO thin films grown at high laser fluence are Ti rich, whereas thin films grown at low laser fluence are Sr rich. 7,13 By employing positron annihilation lifetime spectroscopy, we explicitly demonstrated that Dc is induced by Sr and Ti vacancies for the high and low fluence regime, respectively. 8 Figure 1 also exemplifies that at a given fluence, e.g., F ¼ 1.5 J/cm 2 , the films can be nearly stoichiometric (D TS ¼ 44 mm) but also extremely non-stoichiometric with a Ti-rich (D TS ¼ 40 mm) or a Sr-rich (D TS ¼ 48 mm) composition, depending on the target-to-substrate distance.…”

“…However, in Ref. 7, it was demonstrated that the Sr/Ti ratio of homoepitaxially grown STO thin films strongly depends on the laser fluence, and that a stoichiometric transfer is only obtained for a certain laser fluence. The fluence dependence of the cation stoichiometry has also been recently confirmed for a variety of perovskite thin films.…”