InP/InGaAs double heterojunction bipolar transistors with BVCEO = 12 V and fmax = 470 GHz

0.25 μm emitter InP/InGaAs double heterojunction bipolar transistors (DHBTs) are presented that simultaneously exhibit a high collector current density (J_c) of more than 3 mA/μm² and high breakdown voltage (BV_CEO) of 12 V. The DHBTs consist of a 30 nm-thick InGaAs base, 250 nm-thick InGaAs/InAlGaAs/InP collector and 150 nm-thick n-doped InP field buffer. Since the doping level of the InP field buffer is relatively high, only the InGaAs/InAlGaAs/InP collector is depleted at low V_CE. Thus, the DHBTs can provide f_t = 173 GHz and f_max = 470 GHz at J_c = 3.5 mA/μm². On the other hand, at a high V_CE, both the InGaAs/InAlGaAs/InP collector and InP field buffer are depleted. Therefore, the effective depletion thickness increases, which results in a BV_CEO of 12 V. These results indicate that the use of the InP field buffer provides both high-speed performance and high BV_CEO.