Significant operating voltage reduction on high-speed GaAs-based heterojunction bipolar transistors using a low band gap InGaAsN base layer

We report the fabrication of double heterojunction bipolar transistors (DHBTs) with the use of a new quaternary InGaAsN material system that takes advantage of a low-energy band gap E_G in the base to reduce operating voltages in GaAs-based electronic devices. InGaP/In_0.03Ga_0.97As_0.99N_0.01/GaAs DHBTs with improved band gap engineering at both heterojunctions exhibit a DC peak current gain over 16 with small active emitter area. The use of the lattice-matched In_0.03Ga_0.97As_0.99N_0.01 (E_G=1.20 eV) base layer allows a significant reduction of the turn-on voltage by 250 mV over standard InGaP/GaAs HBTs, while attaining good high-frequency characteristics with cutoff frequency and maximum oscillation frequency as high as 40 GHz and 72 GHz, respectively. Despite inherent transport limitations at the present time, which penalize peak frequencies, this novel technology provides comparable RF performance to conventional devices with a GaAs control base layer but at much lower operating base-emitter bias conditions. This technical progress should benefit to the next generation of RF circuits using GaAs-based HBTs with lower power consumption and better handling of supply voltages in battery-operated wireless handsets.