High gain AlGaAs/GaAs HBTs grown by MOCVD

We report on a study of the DC characteristics of MOCVD-grown AlGaAs/GaAs HBT structures with C-doped (3-5E19 cm/sup -3/) base layers. Analysis of several series of AlGaAs/GaAs HBTs suggest the DC gain is dependent upon base current only, and that the base current is largely limited by bulk recombination in the neutral base. As part of this study, we have obtained DC gains of /spl sim/250 (@ 1kA/cm/sup 2/) at a base sheet resistance of 330 Ohms/square, which we believe is the highest DC gain ever observed for an AlGaAs/GaAs HBT at this base sheet resistance. Proportionally high DC gains have also been realized in HBTs with base sheet resistance values as low as 115 Ohms/square.