Density Functional Theory Study of Engineering TiS₂ Work Function through Intrinsic Defects and Surface Oxidation for Field-Effect Transistors

TiS2 is a van der Waals-layered semiconductor while being highly susceptible to interstitial Ti (Tii) defects, rendering a high electrical conductivity. Understanding the influence of Tii concentration, surface defects, and thickness dependence on its work function is essential for designing TiS2-based electrodes in field-effect transistor-related applications. In this work, density functional theory is used to investigate the defect, thickness, and substrate effects toward TiS2 work function. Our results demonstrate that TiS2 exhibits a remarkably high work function of 5.75 eV. The high work function is slightly reduced to ∼5.6 eV by Tii defects and is insensitive to thickness and Tii concentration. We further reveal that surface oxidation and chemisorption of Ti-based adparticles are the causes of low measured TiS2 work function (4.0–4.5 eV) in experiments. On the other hand, the work function of TiS2 can be enhanced up to ∼6.1 eV by aluminum oxide (Al2O3) substrate while slightly lowered by Ti and Al defects. Our work provides valuable guidance toward engineering high-work-function electrodes in the semiconductor industry.