Enhanced Gate Reliability in GaN MIS-FETs by Converting the GaN Channel into Crystalline Gallium Oxynitride

We demonstrated the enhanced threshold voltage (VTH) stability and gate reliability of the enhancement-mode (E-mode) GaN-based MIS-FETs under reverse-bias stress (i.e., stress at off-state with high drain voltage), which is achieved by converting the conventional GaN (Eg ∼ 3.4 eV) channel into a crystalline GaOxN1–x (Eg ∼ 4.1 eV) layer. In the MIS-FETs stressed at off-state with a large drain voltage, holes will be generated in the high-electric-field region by impact ionization, and subsequently, degradation of the gate dielectric is caused by the holes passing through the dielectric film. As the valence band offset between the GaOxN1–x and GaN is ∼0.6 eV, an energy barrier for holes will be formed surrounding the gate, which can prevent holes from flowing to the gate side and therefore reduce the hole-induced gate dielectric degradation. The crystalline gallium oxynitride layer converted from GaN could also be a promising method to improve channel reliability for many GaN-based structures and processes.