InAlAs/InP/InGaAs/InP DHBTs with a novel composite-emitter design

We report the design and performance of InAlAs/InP/InGaAs/InP double heterostructure bipolar transistors (DHBTs) with a composite-emitter (CE) design. The CE-DHBT structure combines various advantages of conventional InAlAs/InGaAs and InGaAs/InP HBTs. It allows passivation of the extrinsic base with a selective etch, and also allows the possibility of enhancing performance through nonequilibrium transport in the base. The CE-DHBT structure demonstrated an offset voltage (/spl Delta/V/sub CE0/) of 0.25 V with a saturation voltage (V/sub SAT/) of 0.6 V and a dc current gain of 25 for a base doping level of 7/spl times/10/sup 19/ cm/sup -3/.