Abstract
Normally-off AlGaN/GaN MIS-HEMTs with a high threshold voltage (<inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula>) more than 2.5 V and a low on- resistance of <inline-formula> <tex-math notation="LaTeX">$5.5\Omega \cdot $ </tex-math></inline-formula>mm have been achieved by an improved regrowth technique with <i>in-situ</i> SiN<sub><i>x</i></sub> passivation. A thin-barrier heterojunction was used to decrease the two-dimensional electron gas (2DEG) underneath the gate, then regrown Al<sub>0.2</sub>Ga<sub>0.8</sub>N and <i>in-situ</i> SiN<sub><i>x</i></sub> were applied to recover 2DEG at the access regions and reduce contact resistance. The O<sub>3</sub>-based Al<sub>2</sub>O<sub>3</sub> and HfO<sub>2</sub> were employed to cover the recessed-gate with low channel sheet resistances by atomic layer deposition. The other hybrid MIS-HEMT with <i>in-situ</i> SiN<sub><i>x</i></sub> gate interlayer also enabled a normally-off operation with a <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> hysteresis lower than 30 mV. The damage-free recessed-gate structures with in- situ SiN<sub><i>x</i></sub> as passivation and gate dielectric contribute to reducing surface scattering and interface states, resulting in a high <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> uniformity and channel mobility, low on- resistance and<sub>th</sub> hysteresis in normally-off GaN-based MIS-HEMTs.
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