24.4 W/mm X-Band GaN HEMTs on AlN Substrates With the LPCVD-Grown High-Breakdown-Field SiNx Layer

This paper reports on an AlGaN/GaN high-electron-mobility transistor (HEMT) on free-standing AlN substrates with a record-high output power density of 24.4 W/mm at the X-band. A high-drain current operation of 1.4 A/mm was realized by employing high-density 2-dimensional electron gas channel and regrown Ohmic contacts. Furthermore, a high-voltage operation of 110 V was achieved owing to the high-density and high-breakdown SiNx layer grown by low-pressure/high-temperature chemical vapor deposition. Three-stage AlGaN buffer layers improved the electron mobility of 2-dimensional electron gas and allowed us to grow a GaN channel with a low carbon concentration. Furthermore, a regrown n-GaN contact layer was employed to minimize source/drain contact resistances. A high drain current of 1470 mA/mm and high breakdown voltage of 258 V were achieved. Our results demonstrate the potential of GaN HEMTs on the AlN substrate as next-generation high-power radio frequency devices.