Grain size, texture, and crystallinity in lanthanum monosulfide thin films grown by pulsed laser deposition

We report a detailed investigation of the growth of lanthanum monosulfide (LaS) thin films by pulsed laser deposition on (001) magnesium oxide (MgO) substrates in a background of H2S for the purpose of optimizing their crystallinity, texture, and grain size. A variety of films were grown while varying the laser repetition rate, the temperature of the substrate, and the partial pressure of H2S. The thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, and high resolution transmission electron microscopy. Films grown at 500°C with a H2S background pressure of 3.4×10−4Pa and a laser repetition rate of 8Hz produced the LaS film with the largest grains whose size averaged 293nm. The XRD pattern of these films revealed that their orientation was predominantly (200). AFM images of the surface of these films showed large plate-like grains. This contrasts with the fine grain structure observed in LaS films grown at a lower substrate temperature and lower H2S pressure. ► LaS thin films were grown by pulsed laser deposition on MgO substrates in H2S. ► Deposition parameters were substrate temperature, H2S pressure and repetition rate. ► Film crystallinity, texture, and grain size were investigated. ► The growth conditions for optimal texture and grain size are reported.