Performance enhancement by using the n/sup +/-GaN cap layer and gate recess technology on the AlGaN-GaN HEMT fabrication

Due to the low mobility and wide bandgap characteristics of the undoped AlGaN layer used in the conventional AlGaN-GaN HEMT as a cap layer, the RF performance of this device will be limited by its high contact resistance and high knee voltage. We propose using the n/sup +/-GaN cap layer and the selective gate recess etching technology on the AlGaN-GaN HEMTs fabrication. With this n/sup +/-GaN instead of the undoped AlGaN as a cap layer, the device contact resistance is reduced from 1.0 to 0.4 /spl Omega//spl middot/mm. The 0.3 μm gate-length device demonstrates an I/sub ds,max/ of 1.1 A/mm, a g/sub m,max/ of 220 mS/mm, an f
_T
of 43 GHz, an f
_max
of 68 GHz, and an output power density of 4 W/mm at 2.4 GHz.