Investigation of a Hybrid Approach for Normally-Off GaN HEMTs Using Fluorine Treatment and Recess Etch Techniques

A hybrid approach for obtaining normally off high electron mobility transistors (HEMTs) combining fluorine treatment, recess etch techniques, and AlGaN buffer was studied. The effects of process variations (recess etch depth and fluorine treatment duration) and epitaxial differences (AlGaN and carbon doped GaN buffers) on the DC characteristics of the normally off HEMTs were investigated. Two different epitaxial structures and three different process variations were compared. Epitaxial structures prepared with an AlGaN buffer showed a higher threshold voltage (Vth= +3.59 V) than those prepared with a GaN buffer (Vth= +1.85 V).