We report for the first time the design, process and characterization of InP-based micrometer emitter InGaAlAs/GaAsSb/InP Double HBTs (DHBTs) and their microwave performance. The layer structure not only allows the implementation of InP collector free of current blocking, but also enables small turn-on voltage and ballistic launching of electrons due to the positive conduction band discontinuity of emitter to base. The DHBT structure was grown on nominal (001) InP substrates using MBE. Solid Si and CBr4 gas were used for n-type and p-type doing respectively. Fabricated large DHBTs showed high DC gain (> 80), small turn-on voltage 0.62V, almost zero offset voltage, and nearly ideal base and collector current characteristics (ideality factors ∼ 1.0 for both B-E and B-C junctions). Small DHBTs demonstrated VCEO > 8V and stable operation at high current density exceeding 100kA/cm 2. Maximum fT of 57 GHz and maximum fmax of 66 GHz were achieved from 1 × 20 μm2 devices at similar bias condition: JC = 8.0 × 104A/cm2 and V CE =3.5 V. The InGaAlAs/GaAsSb/InP DHBTs appear to be a very promising HBT solution having simultaneous excellent RF and DC performances.
