Evaluation of carbon incorporation in sulfide thin films grown by hybrid pulsed laser deposition

Vapor-pressure mismatched materials (materials whose constituent elements have significantly different vapor pressures) such as transition metal chalcogenides have emerged as electronic, photonic, and quantum materials with scientific and technological importance. While hybrid pulsed laser deposition (hPLD) has emerged as a method for epitaxial or textured growth of vapor-pressure mismatched materials, carbon (C) incorporation has been a persistent concern—especially in instances where organic chalcogen precursors are desired as a less hazardous alternative to more toxic chalcogen hydrides. However, the underlying mechanisms of such unintentional C incorporation and the effects on film growth and properties in hPLD are still elusive. Here, we report on the influence of C-containing side-products of organosulfur precursor pyrolysis in ZnS, BaTiS3, and TiS2 thin films grown by hPLD using a tert-butyl disulfide (TBDS) precursor. By combining the structural characterization of x-ray diffraction (XRD) and atomic force microscopy with secondary ion mass spectrometry, we systematically investigate the role of temperature and TBDS partial pressures on film morphology and crystallinity. ZnS, TiS2, and BaTiS3 have optimal growth temperatures of 400 °C, 500 °C, and 700 °C, respectively, and we observe that samples grown at temperatures above or below have increased C incorporation in the bulk and interface of the film, which correlates with poorer texture of the films as determined by XRD. On the other hand, highly textured films have minimal C at the film-substrate interface and within the film, which are comparable to films grown without TBDS in nominal vacuum conditions. We report TiS2 growths with C incorporation dependent on TBDS growth pressure and determine that 10−1 Pa TBDS is the optimal growth pressure for minimal C contamination. At partial pressures greater than 10−1 Pa, there is no preferential texture of the film, which is possibly caused by the graphitization of C, poisoning the interface and bulk of the film. This work opens opportunities for further understanding process-induced C impurity presence in the hPLD grown thin film transition metal chalcogenides and chalcogenide perovskites and might have important implications for sulfide-based thin film technological applications.