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

We theoretically investigate the grain size dependence of the mobility of WSe2 FETs, and the experimental results which have been recently reported. A larger grain size (LG) WSe2 has been modeled by a single monolayer WSe2 of infinite length. We model a smaller grain size (SG) WSe2 as a partial monolayer of WSe2 with a zigzag edge WSe2 nanoribbon. Our results show that the step edges of the partial monolayer WSe2 function as electron traps. Moreover, the effective mass of SG WSe2 appears to be much larger than that of LG WSe2 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 WSe2 are much lower than those of the LG WSe2. Hence, our calculated results indicate that LG fabrication is essential for advanced large-scale integration (LSI) using WSe2 FETs. (c) 2024 The Japan Society of Applied Physics. All rights, including for text and data mining, AI training, and similar technologies, are reserved.