Effects of Trapped Charges in Gate Dielectric and High-k Encapsulation on Performance of MoS2 Transistor

The effects of trapped charges in gate dielectric and high-k encapsulation layer on the performance of MoS2 transistor are investigated by using SiO2 with different thicknesses as the gate dielectric and HfO2 as the encapsulation layer of the MoS2 surface. Results indicate that the positive trapped charges in SiO2 can increase the electrons in MoS2 for screening the scattering of charged impurity (CI) in SiO2 and at the SiO2/MoS2 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 HfO2 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 HfO2. 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.