Si3N4/Al2O3 Stack Layer Passivation for InAlAs/InGaAs InP-Based HEMTs With Good DC and RF Performances

This paper introduces a novel surface passivation using Si
₃
N
₄
(20-nm)/Al
₂
O
₃
(15-nm) stack layers in InAlAs/InGaAs InP-based high-electron-mobility transistors (HEMTs). The new technology gives rise to good dc and RF performances in InP-based HEMTs. Notably different from the conventional Si
₃
N
₄
approach, an ultrathin layer of Al
₂
O
₃
(15-nm) grown by atomic layer deposition is incorporated in the surface passivation, which is the main feature of this technology. After passivation, the Si
₃
N
₄
/Al
₂
O
₃
-passivated HEMTs exhibit a superior dc performance demonstrating a high drain current up to 800 mA/mm, an increased peak transconductance of 1100 mS/mm at V
_GS
= -0.2 V and a slight threshold voltage shift of ΔV
_th
= +120 mV. In terms of their RF performance, a maximum oscillation frequency (f
_max
) up to 340 GHz has been obtained, showing an excellent quality of the surface passivation. A physical explanation is addressed over why the good dc and RF performances have been achieved.