Sensitive Bandgap Reduction of SrTiO3 Through Incorporation of Sulfur Using Ion Implantation

SrTiO 3 (STO) is a well‐known perovskite oxide often used, among others, as a crystalline substrate for epitaxial deposition. However, its indirect bandgap of 3.25 eV is too high for solar applications. Tentative experiments to reduce its bandgap are very welcome. To this end, we performed sulfurization of STO substrates using ion implantation. The simulated profile is controlled by Time‐of‐Flight Secondary Ion Mass Spectrometry (TOF‐SIMS). We demonstrate that S is at least partially inserted into the STO lattice, as evidenced by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). UV‐visible spectroscopy indicates a drastic reduction of the bandgap of S:STO from 3.25 eV (indirect) down to 2.14 eV for 10% S:STO, a trend also observed by spectroscopic ellipsometry. We confront the results to ab initio calculations. Besides bandgap, the valence band level, that is the ionization energy, was determined by Ambient‐Pressure Photoemission Spectroscopy (APS) so that the complete energy diagrams could be plotted. This work paves the way for tuning the bandgap of perovskites in a highly controlled manner for solar energy applications. This article is protected by copyright. All rights reserved.