Improved performance of MoS₂ FET by In-situ NH₃ Doping in ALD-Al₂O₃ Dielectric

Abstract Since the defects such as traps and oxygen vacancies exist in the dielectric, it is difficult for fabricating high-performance MoS2 FET using atomic-layer-deposition (ALD) Al2O3 as gate dielectric layer. In this paper, NH3 in-situ doping, one kind of process treatment approach during ALD-grown Al2O3, is used to decrease these defects for better device characteristics. The MoS2 FETs with this technique have been well fabricated and the effect of different NH3 in-situ doping sequences among growth cycles are investigated in detail. Compared with general counterparts, the devices with NH3 in-situ doping demonstrate obvious performance enhancements: the I on/I off is improved by one order of magnitude, from 1.33×105 to 3.56×106, and the threshold voltage shifted from -0.74 V to -0.12 V, and a small subthreshold swing of 105mV/dec is achieved. The improvements of MoS2 FET performance are attributed to N-doping by the introduction of NH3 during the Al2O3 ALD-growth process, which leads to the reduction of surface roughness of the dielectric layer and the repair of the oxygen vacancies in the Al2O3 layer. Furthermore, the MoS2 FET with in-situ NH3 doping introduced after Al and O precursors filling cycles demonstrated the best performance, which may be because that NH3 final doping after film growth restores more oxygen vacancies to screen more charge scattering in the MoS2 channel. The reported method provides one promising method to reduce charge scattering in carrier transport for highperformance MoS2 devices.