Effects of trapped charges in gate dielectric and high- k encapsulation on performance of MoS2 transistor

Abstract

The effects of trapped charges in gate dielectric and high-k encapsulation layer on the performance of MoS 2 transistor are investigatedby using SiO 2 with different thicknesses as the gate dielectric and HfO 2 as the encapsulation layer of the MoS 2 surface. Results indicate that the positive trapped charges in SiO 2 can increase the electrons in MoS 2 for screening the scattering of charged impurity (CI) in SiO 2 and at the SiO 2 /MoS 2 interface to increase the carrier mobility. However, the CI scattering becomes stronger for thicker gate dielectric with more trapped charges and can dominate the electron screening effect to reduce the mobility. On the other hand, with the HfO 2 encapsulation, the OFF-currents of the devices greatly increase and their threshold voltages shift negatively due to more electrons induced by more positive charges trapped in HfO 2 . Moreover, the screening effect of these electrons on the CI scattering results in a mobility increase, which increases with the magnitude of the CI scattering. A 51% improvement in mobility is obtained for the sample suffering from the strongest CI scattering, fully demonstrating the effective screening role of high-k dielectric on the CI scattering.