Seebeck Domain Formed by Grain Boundaries of 1H-MoS₂

1H-MoS₂ is a potential candidate material for next-generation electronic devices due to its intrinsic band gap. However, grain boundaries are frequently formed during the synthetic process, reducing the mobility considerably and thus being obstacles for the real application. Understanding the characteristics of this dislocation is essential not just for facilitating large-scale growth, but also in a way that it opens up a new possibility of utilizing a defect itself. The formation of localized states inside a band gap by dislocations at grain boundaries is well known, which are accompanied by the magnetism that is sensitive to the doping and tilt angle. Despite its importance, however, comprehensive investigation of the grain boundary’s electronic structure is limited.<br/>Here, we show the properties of a localized defect state and an inherently induced in-plane dipole field in grain boundaries of 1H-MoS₂ using <i>ab initio</i> calculations. At the grain boundary of single-layer MoS₂, the dipole is observed. Although the field is most visible in the pentagon-heptagon 5|7 dislocation, its presence is not confined to a certain type of defect. We focus our discussion on 5|7 double boundary cell with periodic boundary conditions, which has three particular deep level defect states. These states are localized in a specific boundary dislocation, and two of them have an antibonding nodal line through the center of the defect line.<br/>Furthermore, our <i>ab initio</i> based scanning Seebeck microscope (SSM) simulation demonstrates that the distinctive Seebeck domain of opposite sign is formed around the grain boundaries of 1H-MoS₂. Although it is commonly known that the intrinsic dipole field plays a crucial role in determining the sign of the domain, we found that the impact of the defect level is so massive that it could drastically change the Seebeck value, even the inversion of charge carrier type could locally happen. Another indication of the influence of defects state is the thin line following the nodal line of defect states. Through the antibonding line where the effect of defect states vanishes, a sharp line with an opposite Seebeck sign is easily observed. This result implies that in a polycrystalline system, one should carefully determine the influence of the deep level state before interpreting the meaning of the Seebeck coefficient. Moreover, the delicate engineering of grain boundary may allow the microscopic control of the Seebeck value. Our results suggest that the formation of nanoscale p-n junction or the application of a thin line of the inverted charge carrier type could also be done.