Ultralow Resistance Ohmic Contacts for p-Channel InGaSb Field-Effect Transistors

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 4x reduction in contact resistance compared with a standard p^±-InAs cap. This translates into nearly 3x improvement in the gm of fabricated InGaSb p-channel QW-FETs. Furthermore, Ni contacts on the composite cap were fabricated and a contact resistance of 45 Ω · 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 Ω · cm².