AVS 52nd International Symposium
    Electronic Materials and Processing Wednesday Sessions
       Session EM-WeA

Paper EM-WeA2
Non-uniform Interfacial Reactions of Ti/Al/Mo/Au Ohmic Contacts on n-AlGaN/GaN Heterostructure and its Effect on Carrier Transport

Wednesday, November 2, 2005, 2:20 pm, Room 309

Session: Contacts to Semiconductors
Presenter: L. Wang, University of Illinios at Urbana-Champaign
Authors: L. Wang, University of Illinios at Urbana-Champaign
F.M. Mohammed, University of Illinios at Urbana-Champaign
I. Adesida, University of Illinios at Urbana-Champaign
Correspondent: Click to Email
Ti/Al/Mo/Au multilayer metallization scheme has been demonstrated to have low ohmic contact resistance, high thermal stability, and sharp edge acuity on AlGaN/GaN high electron mobility transistors (HEMT). Transmission electron microscopy (TEM) is used to elucidate the cross-sectional interfacial microstructure and to gain insight into the formation mechanism of low-resistance ohmic contacts. It has been observed that reactions between the metallization and the AlGaN layer did not proceed uniformly. Localized penetration through AlGaN layer up to a depth of 130 nm was observed. Thinning of the AlGaN layer was noted where there was no penetration. Energy dispersive x-ray spectroscopy (EDS), and high resolution TEM (HRTEM) analysis confirmed that the reaction products were TiN. A strong correlation between the appearance of TiN islands and threading dislocations in the epitaxial layers was observed. Further analysis indicated that threading dislocations served as short-circuit diffusion channels, and thus are responsible for the non-uniform reaction. TiN islands have a large total area of intimate contact with the two-dimensional electron gas (2DEG), and since no tunneling of electron through the AlGaN is required, a low resistance ohmic contact is obtained. Methods for promoting and controlling the non-uniform interfacial reaction are proposed.