Effect of deep-acceptor density in buffer layer on breakdown voltage of AIGaN/GaN HEMTs with high-k passivation layer

We make a numerical analysis of breakdown characteristics of AIGaN/GaN HEMTs with a high-k passivation layer, where a deep acceptor above the midgap is considered in a buffer layer and its density N_DA is varied between 10¹⁷ and 3×l0¹⁷ cm^-3. It is shown that, generally, the breakdown voltage V_br becomes higher when the relative permittivity of the passivation layer ϵ_r is higher. In the case where N_DA is relatively low, V_br is determined by impact ionization of carriers when ϵ_τ, is low, but it becomes determined by buffer leakage current when ϵ_τ is high, and V_br becomes saturated with increasing ϵ_r. On the other hand, when N_da is relatively high, V_br is determined by impact ionization of carriers even if ϵ_τ becomes 60, and it becomes about 500 V at the gate-to-drain distance of 1.5 μm, which corresponds to an average electric field of over 3 MV/cm.