Comparative study of Ti/Al and Ti/Al/Ti/Au ohmic contacts to AlGaN/ GaN heterostructures

Abstract

We investigated the electrical properties and the ohmic contact formation considering Ti/Al and Ti/Al/Ti/Au ohmic contact metallization schemes on AlGaN/GaN heterostructures. The specific contact resistance of contacts was determined by characterizing the current-voltage relation from TLM measurement. The lowest value for the specific contact resistivity was obtained using Ti/Al/Ti/Au metallization. An interfacial TiN layer was monitored at the contact-AlGaN interface. TiN phases were found at both contacts, but the thickness in the Ti/Al/Ti/Au contact reached 8 nm, while the thickness in Ti/Al was thinner and discontinuous. The surface roughness of the Ti/Al/Ti/Au contact was determined as 8.17 nm and that of the Ti/Al contact as 36.23 nm. It was found that the spesific contact resistance depends on the atomic structure of the metal-semiconductor interface and composition and structure of the ohmic contact layers. These results showed that it is possible to achieve higher reliability and uniformity as well as lower contact resistance in AlGaN/GaN HEMTs with Ti/Al/Ti/Au contact compared to Ti/Al contact.