ABSTRACT
The growth and characterization of high gain NpN HBTs on GaAs with a pseudomorphic GaAs.92Sb.08 base layer are reported. The layers were grown in an elemental source MBE system, using tetramer As4 and Sb4 sources. The emitter to base heterojunction was abrupt. The HBTs fabricated were large area, mesa isolated transistors, with a beta of 150 at a current density of 2 KA/cm2, and high gain down to low current densities. The specific contact resistance of the refractory base contact has been measured to be as low as 6×10−7 Ωcm2. The turn-on voltage, VBE at JE= 2 A/cm2, is 0.98V. Perhaps most significant, the inclusion of Sb in the base dramatically reduces the diffusion of Be from the base into the wider band gap AlGaAs emitter.
