Band edge states, intrinsic defects, and dopants in monolayer HfS₂ and SnS₂

Although monolayer HfS₂ and SnS₂ do not have a direct bandgap like MoS₂, they have much higher carrier mobilities. Their band offsets are favorable for use with WSe₂ in tunnel field effect transistors. Here, we study the effective masses, intrinsic defects, and substitutional dopants of these dichalcogenides. We find that HfS₂ has surprisingly small effective masses for a compound that might appear partly ionic. The S vacancy in HfS₂ is found to be a shallow donor while that in SnS₂ is a deep donor. Substitutional dopants at the S site are found to be shallow. This contrasts with MoS₂ where donors and acceptors are not always shallow or with black phosphorus where dopants can reconstruct into deep non-doping configurations. It is pointed out that HfS₂ is more favorable than MoS₂ for semiconductor processing because it has the more convenient CVD precursors developed for growing HfO₂.