Improved interfacial and electrical properties of few-layered MoS2 FETs with plasma-treated Al2O3 as gate dielectric

ALD Al2O3 films treated respectively by N2, O2 and NH3 plasmas are used as gate dielectrics to fabricate few-layered MoS2 FETs. As compared with the control sample without any plasma treatment, the devices with different plasmas treatments achieve better electrical properties, with the NH3-treated device having the best results: highest carrier mobility of 39.3 cm2/Vs (~1.65 times higher than that of the control sample), smallest subthreshold swing of 90.9 mV/dec, largest on/off ratio of 1.5 × 107 and negligible hysteresis. These are attributed to the fact that the NH3 plasma treatment can (1) effectively passivate the oxygen vacancies in Al2O3 and decrease the dangling bonds at the Al2O3 surface, thus reducing the traps at/near the Al2O3/MoS2 interface; (2) increase the k value of the dielectric by N incorporation to enhance the screening effect on the Coulomb impurity scattering. In addition, these plasma treatments can adjust the MoS2 FET from depletion mode to enhancement mode by introducing negative ions into the gate dielectric.