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

TL;DR

This study investigates how unintentional carbon incorporation occurs during hybrid pulsed laser deposition of sulfide thin films, revealing optimal growth conditions that minimize contamination and improve film quality.

Contribution

It provides a systematic analysis of carbon incorporation mechanisms in hPLD-grown sulfide films and identifies growth parameters that reduce contamination.

Findings

Optimal growth temperatures vary for different sulfide materials.

Carbon incorporation increases outside optimal temperature ranges.

Higher TBDS pressure leads to more carbon contamination and loss of texture.

Abstract

Vapor-pressure-mismatched materials, such as transition metal chalcogenides, have emerged as key electronic, photonic, and quantum materials. Hybrid pulsed laser deposition (hPLD) has become a preferred method for epitaxial or textured growth of these materials; however, unintentional carbon (C) incorporation remains a persistent concern, particularly when using organic chalcogen precursors as safer alternatives to toxic hydrides. The mechanisms governing C incorporation and its impact on film growth and properties in hPLD remain poorly understood. Here, we investigate the influence of C-containing side products generated from organosulfur precursor pyrolysis on ZnS, BaTiS$_3$, and TiS$_2$ thin films grown by hPLD using tert-butyl disulfide (TBDS). Structural characterization via X-ray diffraction and atomic force microscopy, combined with secondary ion mass spectrometry, is used to systematically examine the effects of growth temperature and TBDS partial pressure on film morphology, crystallinity, and C incorporation. Optimal growth temperatures of 400{\deg}C, 500{\deg}C, and 700{\deg}C are identified for ZnS, TiS$_2$, and BaTiS$_3$, respectively. Growth above or below these temperatures leads to increased C incorporation at both the interface and within the film, correlating with degraded texture. In contrast, highly textured films exhibit minimal C content, comparable to films grown without TBDS. For TiS$_2$, C incorporation depends strongly on TBDS pressure, with 10$^{-1}$ Pa identified as the optimal pressure for minimizing contamination. At higher pressures, loss of preferential texture is observed, likely due to C graphitization poisoning the interface and bulk. These results provide new insight into process-induced C impurities in hPLD-grown chalcogenide thin films and have important implications for sulfide-based thin film technologies.