Improved performance of MoS₂ FET by in situ NH₃ doping in ALD Al₂O₃ dielectric

Since defects such as traps and oxygen vacancies exist in dielectrics, it is difficult to fabricate a high-performance MoS_2 field-effect transistor (FET) using atomic layer deposition (ALD) Al_2O_3 as the gate dielectric layer. In this paper, NH_3 in situ doping, a process treatment approach during ALD growth of Al_2O_3, is used to decrease these defects for better device characteristics. MoS_2 FET has been well fabricated with this technique and the effect of different NH_3 in situ doping sequences in the growth cycle has been investigated in detail. Compared with counterparts, those devices with NH_3 in situ doping demonstrate obvious performance enhancements: I_\rm on/I_\rm off is improved by one order of magnitude, from 1.33\times 10^5 to 3.56\times 10^6, the threshold voltage shifts from -0.74 V to -0.12 V and a small subthreshold swing of 105 mV/dec is achieved. The improved MoS_2 FET performance is attributed to nitrogen doping by the introduction of NH_3 during the Al_2O_3 ALD growth process, which leads to a reduction in the surface roughness of the dielectric layer and the repair of oxygen vacancies in the Al_2O_3 layer. Furthermore, the MoS_2 FET processed by in situ NH_3 doping after the Al and O precursor filling cycles demonstrates the best performance; this may be because the final NH_3 doping after film growth restores more oxygen vacancies to screen more charge scattering in the MoS_2 channel. The reported method provides a promising way to reduce charge scattering in carrier transport for high-performance MoS_2 devices.