Common Emitter Current Gain >1 in III-N Hot Electron Transistors With 7-nm GaN/InGaN Base

Current gain is demonstrated in III-N hot electron transistors (HETs) for the first time using base current controlled common emitter characteristics. The emitter and collector barriers (ØBE and ØBC) are implemented using AlN and In
_0.1
Ga
_0.9
N layers as polarization-dipoles, respectively. The entire structure is grown by plasma-assisted molecular beam epitaxy. Current gain is observed when the base thickness is reduced from 13 to 7 nm. Ohmic contacts to the base 2-D electron gas (2DEG) are achieved using a BCl
₃
/SF
₆
etch to remove the emitter and selectively stop on the AlN. Subsequent metallization results in a tunnel contact from the metal to the base 2DEG across the thin AlN layer. This dual purpose served by the AlN layer is shown to be critical for achieving scaled base and current gain in III-N HETs.