Analysis of Atomistic Dopant Variation and Fermi Level Depinning in Nanoscale Contacts

Using quantum transport simulations of metal-semiconductor junctions, we assess the viability of barrier thinning with dopants and barrier lowering with interfacial layers as solutions for contact resistivity in nanoscale transistors. Our atomistic simulations show that the discreteness of dopants leads to increasing variability in contact resistance as dimensions scale below 10 nm. We find that the use of interlayers can counteract low doping caused by atomistic variation, but the interlayer must have band edge Fermi level pinning to provide a net reduction in contact resistivity. For materials with low doping limits, such as n-type germanium, we find that interlayer contacts still have difficulty meeting resistivity targets.