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 Si₃N₄ (20-nm)/Al₂O₃ (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 Si₃N₄ approach, an ultrathin layer of Al₂O₃ (15-nm) grown by atomic layer deposition is incorporated in the surface passivation, which is the main feature of this technology. After passivation, the Si₃N₄/Al₂O₃-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.