Impact of grain size on the performance of WSe₂ FETs revealed by first-principles calculations

Abstract We theoretically investigate the grain size dependence of the mobility of WSe 2 FETs, and the experimental results which have been recently reported. A larger grain size (LG) WSe 2 has been modeled by a single monolayer WSe 2 of infinite length. We model a smaller grain size (SG) WSe 2 as a partial monolayer of WSe 2 with a zigzag edge WSe 2 nanoribbon. Our results show that the step edges of the partial monolayer WSe 2 function as electron traps. Moreover, the effective mass of SG WSe 2 appears to be much larger than that of LG WSe 2 because of hybridization with gap states originating from step edges at the conduction band minimum. These results coincide with recent experiments that show that the on-currents of the SG WSe 2 are much lower than those of the LG WSe 2 . Hence, our calculated results indicate that LG fabrication is essential for advanced large-scale integration (LSI) using WSe 2 FETs.