Gate-Recessed Normally-OFF GaN MOSHEMT With Improved Channel Mobility and Dynamic Performance Using AlN/Si 3 N 4 as Passivation and Post Gate-Recess Channel Protection Layers

In this letter, a gate recessed normally-off GaN metal–oxide–semiconductor high-electron-mobility transistor on silicon substrate is fabricated using AlN/Si 3 N 4 as the passivation layer. The thin AlN layer serves the dual role of protecting the gate channel region from direct plasma bombardment during the RIE Si 3 N 4 removal and passivating the surface states in the access region. As a result, the effective carrier mobility in the normally-off channel is found to improve from the 568 cm 2 / $\text {V}\cdot \text {s}$ in conventional Si 3 N 4 passivation process to a high value of 1154 cm 2 / $\text {V}\cdot \text {s}$ . A saturated output current density of 603 mA/mm and an ON-resistance of $5.3~\Omega \cdot \text {mm}$ was obtained for devices with $\text{L}_{\text {G}}/\text{L}_{\text {GS}}/\text{L}_{\text {GD}}/\text{W}_{\text {G}} = 1.5$ /1.5/3/ $20~\mu \text{m}$ . Meanwhile, the degradation of dynamic ON-resistance is significantly suppressed due to the effective passivation of surface states by the AlN layer grown by plasma-enhanced atomic layer deposition.