Gate-Recessed Normally-OFF GaN MOSHEMT With Improved Channel Mobility and Dynamic Performance Using AlN/Si3N4 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
/V · s in conventional Si
₃
N
₄
passivation process to a high value of 1154 cm
²
/V· s. A saturated output current density of 603 mA/mm and an ON-resistance of 5.3 Ω · mm was obtained for devices with L
_G
/L
_GS
/L
_GD
/W
_G
= 1.5/1.5/3/20 μm. 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.