Composite-Collector InGaAs/InP Double Heterostructure Bipolar Transistors with Current-Gain Cutoff Frequency of 242 GHz

To eliminate the conduction band spike at the base-collector interface, an InP/InGaAs double heterostructure bipolar transistor (DHBT) with an InGaAsP composite collector is designed and fabricated using the conventional mesa structure. The DHBT with emitter area of 1.6×15μm² exhibits current-gain cutoff frequency f_t = 242GHz at the high collector current density J_C=2.1mA/μm², which is to our knowledge the highest f_t reported for the mesa InP DHBT in China. The breakdown voltage in common-emitter configuration is more than 5V. The high-speed InP/InGaAs DHBT with high current density is very suitable for the application in ultra high-speed digital circuits.