Extended Data Fig. 5: Transconductances of ballistic InSe FETs.

a, Transfer characteristics for ten typical ballistic InSe FETs at V_DS = 0.5 V. The dashed line is the theoretically calculated transfer curve³⁹. b, Corresponding transconductance of ten typical ballistic InSe FETs at V_DS = 0.5 V. The best transconductance is 6 mS μm⁻¹. Six FETs have transconductances exceeding 4 mS μm⁻¹. The dashed line is the theoretically calculated transconductance³⁹. c,d, Transfer curve and output of a typical ballistic InSe FET (with a transconductance of 6 mS μm⁻¹). e, Transfer characteristics of a typical ballistic 2D InSe FET with 20-nm channel length at V_DS = 0.1, 0.3, 0.5 and 0.7 V. f, Transfer characteristics comparison of ballistic 2D InSe FET at V_DS = 0.5 and 0.7 V (coloured dots), 10-nm-node silicon FinFET (Intel, solid black line) and 20-nm-L_G InGaAs FinFET normalized by state-of-the-art Fin Pitch = 34 nm (IBM, dashed black line). Note that all currents are normalized with the same rule. g, Transconductances comparison of typical ballistic 2D InSe FETs, a 10-nm-node silicon FinFET (Intel, solid black line) and an InGaAs FinFET (IBM, dashed black line). h, Transconductances comparison of ballistic 2D InSe FET at V_DS = 0.5 and 0.7 V and other 2D FETs with sub-50-nm L_G at V_DD = 1 V. It shows that the transconductance of our InSe FETs at V_DS = 0.7 V reaches 7 mS µm⁻¹, which is larger than that of silicon FETs at the same bias voltage of V_DS = 0.7 V but with slight degraded off-leakage current and subthreshold slope. The large transconductances of our 2D-InSe FETs benefit from several features of our FETs, including the ballistic channel with hardly any scatterings, higher thermal velocity, better source and drain contacts with negligible Schottky barriers and 2.6-nm-thick HfO₂ double-gate structure.