Hole- and electron-injection driven phase transitions in transition metal dichalcogenides and beyond: A unified understanding
Xiao-Huan Lv, Mengqi Wu, Yin‐Ti Ren, Ruining Wang, Hu Zhang, Chendong Jin, Ruqian Lian, Peng-Lai Gong, Xingqiang Shi, Jianglong Wang
Abstract
The phase transitions among polymorphic two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted increasing attention for their potential in enabling distinct functionalities in the same material for making integrated devices. Electron injection to TMDs has been proved to be a feasible way to drive structural phase transition from the semiconducting $H$ phase to the semimetal $dT$ phase. In this paper, based on density functional theory calculations, firstly, we demonstrate that hole injection drives the transition of the $H$ phase more efficiently to the metallic $T$ phase than to the semimetallic $dT$ phase for group-VI-B TMDs (${\mathrm{MoS}}_{2}, {\mathrm{WS}}_{2}, {\mathrm{MoSe}}_{2}$, etc.). The origin can be attributed to the smaller work function (WF) of the $T$ phase than that of the $dT$ phase. Our WF analysis can distinguish the $T$ and $dT$ phases quantitatively, while it is challenging for the commonly used crystal field splitting analysis. In addition, our analysis provides a unified understanding for both hole- and electron-injection induced phase transitions for 2D materials beyond TMDs, such as the synthesized ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ family. Moreover, the hole-driven $T$-phase transition mechanism can explain the recent experiment of ${\mathrm{WS}}_{2}$ phase transition by hole doping with yttrium (Y) atoms. Using $\frac{1}{3}$ Y-doped ${\mathrm{WS}}_{2}$ and ${\mathrm{MoSe}}_{2}$ as examples, we show that the Mo and W valency increases to 5+. These above findings open an avenue to obtain the metallic $T$ phase, which expands the possible stable phases of 2D materials.