Sequential pulsed laser deposition of homoepitaxial SrTiO$_3$ thin films

TL;DR

This study demonstrates precise control of SrTiO$_3$ thin film stoichiometry through sequential pulsed laser deposition from binary-oxide targets, enabling improved film quality and defect management for functional oxide applications.

Contribution

The paper introduces a method for finely tuning SrTiO$_3$ film composition via sequential deposition, establishing a growth window for stoichiometry control and analyzing growth mechanisms.

Findings

Stoichiometry can be precisely controlled by adjusting pulse ratios.

Optimal conditions produce atomically flat, stoichiometric films.

Off-stoichiometry leads to defects, islands, and precipitates.

Abstract

Control of thin film stoichiometry is of primary relevance to achieve desired functionality. Pulsed laser deposition ablating from binary-oxide targets (sequential deposition) can be applied to precisely control the film composition, offsetting the importance of growth conditions on the film stoichiometry. In this work, we demonstrate that the cation stoichiometry of SrTiO$_3$ thin films can be finely tuned by sequential deposition from SrO and TiO$_2$ targets. Homoepitaxial SrTiO$_3$ films were deposited at different substrate temperatures and Ti/Sr pulse ratios, allowing the establishment of a growth window for stoichiometric SrTiO$_3$. The growth kinetics and nucleation processes were studied by reflection high-energy electron diffraction and atomic force microscopy, providing information about the growth mode and the degree of off-stoichiometry. At the optimal (stoichiometric) growth conditions, films exhibit atomically flat surfaces, whereas off-stoichiometry is accommodated by crystal defects, 3D islands and/or surface precipitates depending on the substrate temperature and the excess cation. This technique opens the way to precisely control stoichiometry and doping of oxide thin films.