GSMBE grown In0.49Ga0.51P/GaAs heterojunction bipolar transistors with heavily beryllium doped base and undoped Spacer

Lattice-matched N–p+–n In0.49Ga0.51P/GaAs heterojunction bipolar transistors (HBT's) with heavily beryllium doped base and undoped spacers were grown by gas source molecular beam epitaxy (GSMBE). The epitaxial structure consists of, from the bottom to the top, a 5000Å n+-GaAs sub-collector with Si doping level of 3×1018cm−3, a 7000Å n-GaAs collector doped at concentration of 3×1016cm−3, a 60nm p+-GaAs base with Be doping level up to 3×1019cm−3 inserted between two undoped GaAs spacers, a 100nm N-In0.49Ga0.51P emitter doped at 3×1017cm−3. The structure was completed with a 150nm n+-GaAs cap layer with Si doping level of 3×1018cm−3. Devices with emitter area of 100×100μm were fabricated on the grown wafer by using selective wet chemical etching technique and photolithographic process. AuGeNi/Au was used for the emitter and collector contacts, and Cr/Au was used for the base contact. The turn-on voltages of p+-GaAs/N-In0.49Ga0.51P heterojunction and p+-GaAs/n-GaAs junction are 1.0 and 0.65V. The reverse breakdown voltages of the B–E and B–C junctions are 10 and 12V. The common-emitter current-voltage characteristics show that the maximum current gain reaches 320 at the collector current of 90mA.