Fermi level depinning for the design of III–V FET source/drain contacts

High mobility III–V compounds is a strong contender for extending high performance logic beyond the 22 nm technology node [1–3]. However, demonstrations of exceptional III–V performance required device footprints on the µm-scale despite nm-scale gate lengths, in order to avoid source/drain shorting during contact alloying. The scaling of III–V FETs is severely limited by the unacceptably large lateral diffusion of the multilayer alloyed structures typically used for ohmic contacts [4]. In our recent work, we introduced a novel non-alloyed, highly scalable contact structure through the use of Al as a low workfunction metal on an unpinned Fermi level [5]. We use GaAs as a baseline III–V material, where the developed contact techniques can be extended to InGaAs and InSb, materials which are more technologically important [6]. In this work, we explain in detail the unpinning mechanisms and the rationale for the material selection. We demonstrate the same method can be applied to a variety of metals, Y, Er, Al, Ti, W, and Pt, providing much flexibility in the design of an ideal source/drain contact for III–V HEMTs/MOSFETs and Schottky Barrier FETs.