The fundamental lower limit on the turn-on voltage of GaAs-based bipolar transistors is reduced with the use of a low energy-gap base material, GaInAsN. A 115 mV reduction in the turn-on voltage over a wide range of base sheet resistance values (250 to 850 W/p) is established relative to both GaAs BJTs and conventional InGaP/GaAs HBTs with optimized base-emitter interfaces. InGaP/GaInAsN DHBTs structures with high p-type doping levels
(~ 3x10¹⁹ cm^-3 ) and acceptable DC and RF characteristics (ßmax ~75, f_t ~64 GHz) are demonstrated. The reduction in turn-on Vbe enabled by lattice-matched GaInAsN base layers should permit improved management of the voltage budget, and enhance the overall performance, of both wired and wireless GaAs-based RF circuits.