We demonstrate ultralow ohmic contact resistance to antimonide-based, p-channel quantum-well field-effect transistor (QW-FET) structures using a new p + -InAs/InAsSb cap structure. The incorporation of a p + -InAsSb layer enables the use of a thicker cap with lower sheet resistance, resulting in an improved contact resistivity. Using a Pd-based ohmic scheme, the composite cap structure resulted in a 4× reduction in contact resistance compared with a standard p + -InAs cap. This translates into

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... early 3× improvement in the g m of fabricated InGaSb p-channel QW-FETs. Furthermore, Ni contacts on the composite cap were fabricated and a contact resistance of 45 · μm was obtained. An accurate contact resistivity extraction in this very low range is possible through nanotransmission line models with sub-100 nm contacts. In devices of this kind with Ni-based contacts, we derive an ultralow contact resistivity of 5.2 · 10 −8 · cm 2 .