Enhanced threshold-voltage stability via local strain mitigation in GaN HEMTs with a crystalline SiN/AlN cap

In this study, we proposed a crystalline SiN-capped AlGaN/GaN high electron mobility transistor (HEMT) with an AlN sub-cap layer. Based on geometric phase analysis, the introduction of an AlN sub-cap layer mitigates the strain at the SiN/AlGaN interface, leading to a more uniform strain distribution and high-quality interface characteristics with low interface state density. Compared with the devices without a sub-cap layer or with a gallium nitride (GaN) sub-cap layer, the GaN HEMTs with an AlN sub-cap layer exhibit lower on-resistance and higher electron mobility. Additionally, the devices show an enhanced threshold-voltage stability characterized by the thermal stimulation (ΔVth = −0.05 V at 25 and 150 °C) and the gate-bias stress (ΔVth = 0.02 V during the 1000 s at VGS = 2 V). The high-performance crystalline SiN-capped GaN HEMT with an AlN sub-cap layer demonstrates great potential for the high-reliability power transistors.