High performance InP/GaAsSb/InP DHBTs with heavily doped base layers

We discuss the design and fabrication of high-performance InP/GaAsSb/InP NpN double heterostructure bipolar transistors (DHBTs) grown by MOCVD with heavy carbon doping in the GaAsSb base layer. The staggered (type II) band lineup at InP-GaAsSb heterojunctions allows the growth of abrupt E/B and C/B heterojunctions, thus greatly simplifying the growth and implementation of DHBTs. In addition, C-doped GaAsSb base layers are essentially free of H-passivation effects and can be doped to levels as high as 2.5×10²⁰ cm^-3 while maintaining hole mobilities of at least μ_p=25-30 cm² /Vs for extremely low base sheet resistances. We show that cutoff frequencies in excess of 200 GHz can be achieved while maintaining breakdown voltages ⩾6 V thanks to the low impact ionization coefficients in the InP collector. InP/GaAsSb/InP DHBTs therefore show much potential for ⩾40 Gb/s applications