Thickness-controlled black phosphorus tunnel field-effect transistor for low-power switches

The continuous down-scaling of transistors has been the key to the successful development of current information technology. However, with Moore's law reaching its limits, the development of alternative transistor architectures is urgently needed¹. Transistors require a switching voltage of at least 60 mV for each tenfold increase in current, that is, a subthreshold swing (SS) of 60 mV per decade (dec). Alternative tunnel field-effect transistors (TFETs) are widely studied to achieve a sub-thermionic SS and high I₆₀ (the current where SS becomes 60 mV dec^-1)². Heterojunction (HJ) TFETs show promise for delivering a high I₆₀, but experimental results do not meet theoretical expectations due to interface problems in the HJs constructed from different materials. Here, we report a natural HJ-TFET with spatially varying layer thickness in black phosphorus without interface problems. We have achieved record-low average SS values over 4-5 dec of current (SS_{ave_4dec} ~22.9 mV dec^-1 and SS_{ave_5dec} ~26.0 mV dec^-1) with record-high I₆₀ (I₆₀ = 0.65-1 μA μm^-1), paving the way for application in low-power switches.