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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 MoS2 field-effect transistor (FET) using atomic layer deposition (ALD) Al2O3 as the gate dielectric layer. In this paper, NH3 in situ doping, a process treatment approach during ALD growth of Al2O3, is used to decrease these defects for better device characteristics. MoS2 FET has been well fabricated with this technique and the effect of different NH3 in situ doping sequences in the growth cycle has been investigated in detail. Compared with counterparts, those devices with NH3 in situ doping demonstrate obvious performance enhancements: I on/I off is improved by one order of magnitude, from 1.33 × 105 to 3.56 × 106, 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 MoS2 FET performance is attributed to nitrogen doping by the introduction of NH3 during the Al2O3 ALD growth process, which leads to a reduction in the surface roughness of the dielectric layer and the repair of oxygen vacancies in the Al2O3 layer. Furthermore, the MoS2 FET processed by in situ NH3 doping after the Al and O precursor filling cycles demonstrates the best performance; this may be because the final NH3 doping after film growth restores more oxygen vacancies to screen more charge scattering in the MoS2 channel. The reported method provides a promising way to reduce charge scattering in carrier transport for high-performance MoS2 devices.