Abstract

This thesis presents the fabrication, characterization, and off-state gate leakage simulation of Al x Ga 1−x N/GaN Heterojunction Field-Effect Transistors (HFETs). GaN HFETs are promising devices for high power, high frequency applications such as microwave amplifiers. This is due to the numerous benefits of the GaN material system including high electron mobility, breakdown field, saturation velocity, and thermal conductivity. This thesis is broken down into two major components. The first and most significant covers the fabrication and characterization of Al x Ga 1−x N/GaN HFETs. Devices were fabricated at McGill University’s Nanotools Microfabrication laboratory using a custom designed process flow. This process flow builds on previous work and presents Ohmic contact results of Ti/Al/Ti/Au and Ti/Al/Ti/Al/Ti/Au metalizations. A complete description of the process flow is provided including technology characterization results, such as mesa height profiling, where applicable. Electrical characterization of fabricated devices is performed. Results show an average contact resistance across temperature of 3.39Ωmm for the Ti/Al/Ti/Au metalization and 3.22Ωmm for the Ti/Al/Ti/Al/Ti/Au metalization. Full contact resistance results are provided over
a wide range of temperature. The Ti-Al multi-layer metalization also outperforms the Ti/Al/Ti/Au metalization in terms of drain current density ( 0.12A/mm vs. 0.09A/mm ) and transconductance
( 60mS/mm vs. 40mS/mm ). Off-state gate leakage and current-voltage profiling are also carried out.

The second part of this thesis concerns gate leakage current in Al x Ga 1−x N/GaN HFETs. A new off-state gate leakage model is presented to determine the variation in leakage mechanisms with
the change in barrier layer aluminum mole fraction. A new metric of turning point is introduced to show where Fowler-Nordheim tunneling becomes the dominant leakage mechanism. Results show that as Al mole fraction is increased, the turning point becomes more negative and total gate leakage increases. Finally, improvements to the fabrication process and simulations are presented.