ABSTRACT
In this paper we report on the growth, fabrication and performance of InGaP/GaAs HBTs with a compositionally graded InxGa1-xAs base. In characterizing the carbon-doped strained base layer, the interdependence of indium and carbon incorporation during growth was studied. HBTs with the base graded linearly from GaAs at the emitter-base junction to In xGa1-xAs at the base-collector junction (where x is the highest mole fraction of In in the base) were fabricated and tested. The dc current gain increased by as much as 50% compared to a device with a standard base design (non-graded base). The unity gain cutoff frequency increased from 69 GHz for the standard device to 83 GHz for the graded base device. The maximum frequency of oscillation of the graded base device also increased compared to the standard device from 183 GHz to 197 GHz. These are the highest f t and f max reported to date for InGaP/GaAs HBTs.
