Ohmic Metallizations to Aluminum Gallium Nitride/gallium Nitride High Electron Mobility Transistors: Electrical and Microstructural Studies

Abstract

Major findings of this work include: (1) Elucidated the interfacial reactions between Al, Ti, AlTi alloy, and Ti/Al/Mo/Au on GaN. (2) Explained the electrical performance of Ti/Al/Mo/Au on AlGaN/GaN based on microstructural investigations. Proposed a "spike" mechanism. (3) Identified the role of other metals, i.e. V, Mo, and Ta, as the first layer for X/Al/Mo/Au contacts. (4) Correlated the surface roughness, lateral encroachment, and contact performance of the Ti/Al/X/Au (X=Ni, Pt, Ir, Mo, Ti and NM) contacts for AlGaN/GaN HEMTs. (5) Tailored the interfacial reaction pathways and electrical performance of Ti/Al/Mo/Au on AlGaN/GaN by incorporating Si into the metallization. Obtained low-resistance contact schemes having wide processing window. (6) Investigated the electrical performance and microstructure of the Ti/Al/Mo/Au contacts on all-binary AlN/GaN HEMTs. Optimized the Ti/Al/Mo/Au contacts on n+-GaN capped AlGaN/AlN/GaN by combined surface treatment and solid state interfacial reaction. (7) Evidenced ultra-shallow Si plasma implantation and dry etch effects of SiCl4 pre-metallization treatment. Demonstrated the best performance by side-way direct contact of the metal with the 2DEG channel. (8) Characterized the carrier transport mechanism by variable temperature measurement between 100 and 375 K.