Undoped and Doped Junctionless FETs: Source/Drain Contacts and Immunity to Random Dopant Fluctuation

By using numerical simulations, we demonstrate that a proper source/drain contacting strategy not only boosts the on-currents, but also eliminates random dopant fluctuation (RDF) of a junctionless FET (JLFET). Two contacting strategies for JLFETs with a wide range of doping concentration ($10^{10} \sim ~10^{20}$ cm$^{-3})$ are compared and discussed: metal-insulator-semiconductor (MIS) and metal-semiconductor (MS) contacts. The Schottky barrier at the MS contact shows more negative impacts on the on-current when the JLFET is not doped heavily. With dopantless and unintentionally doped Si (doping concentration $= 10^{10} \sim ~10^{17}$ cm$^{-3}$ for both n-type dopants and p-type dopants), the JLFETs with MIS contacts may exhibit higher on-currents than those with MS contacts and show almost the same transfer characteristics. The later result actually implies that the JLFET with MIS contacts possesses the immunity against RDF.