Normally-OFF AlGaN/GaN MIS-HEMTs With Low RON and Vth Hysteresis by Functioning In-situ SiNx in Regrowth Process

Normally-off AlGaN/GaN MIS-HEMTs with a high threshold voltage ( $\text{V}_{\text {th}}$ ) more than 2.5 V and a low on- resistance of $5.5\Omega \cdot $ mm have been achieved by an improved regrowth technique with in-situ SiN_x passivation. A thin-barrier heterojunction was used to decrease the two-dimensional electron gas (2DEG) underneath the gate, then regrown Al_0.2Ga_0.8N and in-situ SiN_x were applied to recover 2DEG at the access regions and reduce contact resistance. The O₃-based Al₂O₃ and HfO₂ were employed to cover the recessed-gate with low channel sheet resistances by atomic layer deposition. The other hybrid MIS-HEMT with in-situ SiN_x gate interlayer also enabled a normally-off operation with a $\text{V}_{\text {th}}$ hysteresis lower than 30 mV. The damage-free recessed-gate structures with in- situ SiN_x as passivation and gate dielectric contribute to reducing surface scattering and interface states, resulting in a high $\text{V}_{\text {th}}$ uniformity and channel mobility, low on- resistance and_th hysteresis in normally-off GaN-based MIS-HEMTs.