Composite Crystalline Aluminum Nitride Passivation for Near-Junction Thermal Management in Gallium Nitride High-Electron-Mobility Transistors

In this work, we demonstrate a composite crystalline aluminum nitride (AlN) passivation layer for near-junction thermal management in aluminum gallium nitride/gallium nitride (AlGaN/GaN) high-electron-mobility transistors (HEMTs). The 120-nm-thick AlN film consists of an ordered interfacial AlN region together with an upper polycrystalline overlayer. Time-domain thermoreflectance (TDTR) measurements yield an effective cross-plane thermal conductivity of 47.2 W/m·K for the composite AlN, much higher than 2.58 W/m·K for the silicon nitride (SiNx) reference, together with a lower interfacial thermal resistance of 10.0 m2·K/GW compared with 29.6 m2·K/GW for the SiNx-passivated interface. Spatially resolved vibrational electron energy-loss spectroscopy (EELS) further indicates more continuous interfacial vibrational evolution at the AlN/nitride interface. At the device level, steady-state thermoreflectance measurements reveal that the channel-proximal peak temperature is markedly reduced under comparable power densities, accompanied by a more uniform temperature distribution in the gate-to-drain region. In addition to the thermal benefit, the composite AlN layer maintains favorable direct-current (DC) output characteristics relative to the SiNx reference device. These results show that composite crystalline AlN is an effective passivation and near-junction heat-spreading layer for GaN HEMTs.