Mechanism of Linearity Improvement in GaN HEMTs by Low Pressure Chemical Vapor Deposition-SiN_x Passivation

The mechanism of linearity improvement in AlGaN/GaN high-electron mobility transistors (HEMTs) by low pressure chemical vapor deposition (LPCVD)-SiNx passivation is verified using an asymmetric passivation structure, based on different two-dimensional electron gas (2DEG) enhancement capability between LPCVD-SiNx and SiO2 passivation grown by plasma-enhanced CVD (PECVD). The fabricated AlGaN/GaN HEMTs with a hybrid LPCVD-SiNx/PECVD-SiO2 passivation structure deliver a linearity figure of merit third-order intermodulation point (OIP3)/PDC of 4.36 dB, which is 2.84 dB higher than HEMTs with pure PECVD-SiO2 passivation. Benefiting from the charge and electric field modulation effect of the LPCVD-SINx in the source-gate access region of HEMTs, the current-dependent nonlinear source access resistance is remarkably improved, especially at high current level over 500 mA/mm and high temperature. LPCVD-SINx could be a compelling passivation for the fabrication of high linearity GaN-based power HEMTs.