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 (10¹⁰ ∼ 10²⁰ 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 oncurrent when the JLFET is not doped heavily. With dopantless and unintentionally doped Si (doping concentration = 10¹⁰ ∼ 10¹⁷ 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.