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

We demonstrated the enhanced threshold voltage ( V TH ) 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 ( E g ∼ 3.4 eV) channel into a crystalline GaO x N 1– x ( E g ∼ 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 GaO x N 1– 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.