InGaAs/InP DHBTs demonstrating simultaneous ƒτ/ƒmax ∼ 460/850 GHz in a refractory emitter process

We report InP/In
_0.53
Ga
_0.47
As/InP double heterojunction bipolar transistors (DHBTs) demonstrating simultaneous 460 GHz f
_τ
and 850 GHz f
_max
. The devices were fabricated using a triple mesa process with dry-etched, refractory metals for emitter contact formation. The devices incorporate a 35 nm thick InP emitter which enables a wet etch emitter process demonstrating 220 nm wide emitter-base junctions with less than 10 nm undercut in the emitter semiconductor below emitter metal. This reduces the gap between base metal contact and emitter semiconductor causing significant reduction in emitter-base gap resistance (R
_gap
) component of the total base access resistance (R
_bb
), leading to an increase in observed f
_max
. At peak RF performance, the device is operating at 32 mW/μm
²
with J
_e
= 19.4 mA/μm
²
and V
_ce
= 1.66 V. The devices show a DC common emitter current gain (β) ~20 and V
_BR,CEO
= 3.7 V.