NpnN double-heterojunction bipolar transistor on InGaAsP/InP

Double-heterojunction bipolar transistors have been fabricated on InGaAs(P)/InP with current gains of up to 200. Transistors with a p+-InGaAs/N-InP base/collector junction exhibited drastic gain reduction at low collector bias voltages which is ascribed to the electron repelling effect of the conduction-band spike formed at the collector heterojunction. To overcome this complication a thin n-InGaAs transition layer was inserted between the ternary base and the InP wide-gap collector. The resulting nN double-layer collector structure leads to excellent current/voltage characteristics.