High-performance self-aligned InP/InGaAs DHBTs with a passivation ledge utilizing a thin etching stop layer

The relation between effective emitter resistance, r
_e

^eff
, and collector current, I
_C
, was investigated for InGaP/GaAs HBTs and InP/InGaAs DHBTs. While the relation between r
_e

^eff
and I
_C

^-1
of InGaP/GaAs HBT is linear over a wide range of I
_C
, that of InP/InGaAs DHBT is nonlinear as if r
_e

^eff
in the low collector current region increased more than the dynamic emitter resistance component that is proportional to I
_C

^-1
. Although this phenomenon is enhanced in InP/InGaAs DHBTs with a thin InGaAs etching stop layer inserted in the emitter to make it controllable to form a ledge passivation structure, the etching stop layer is acceptable in high-performance high-reliability HBT applications. Using an emitter structure with an etching stop layer, we developed self-aligned InP/InGaAs DHBTs with a passivation ledge structure that attained an f
_T
of 302 GHz, f
_max
of 388 GHz, and BV
_CEO
of 6.2 V.