Fabrication and characterization of high-performance InP/InGaAs double-heterojunction bipolar transistors

This paper is on high-performance InP/InGaAs double-heterojunction bipolar transistors (DHBT´s) utilizing compositionally step-graded InGaAsP layers between the InGaAs base and InP collector to suppress the current blocking effect. These DHBT´s exhibit current gains of 200 and excellent breakdown behavior. Moreover, the DHBT´s permit collector current density levels J_C up to 3×10⁵ A/cm ² at V_CE=1.5 V. A current gain cutoff frequency of 155 GHz and a maximum oscillation frequency of 90 GHz have been successfully obtained at J_C=1.6×10⁵ A/cm². We have also investigated electron transport properties in the InP collector using a set of DHBT´s with different injection energies into the InP collector. By increasing the injection energies, electron velocity is found to decrease from 3.5×10⁷ cm/s to 1.6×10⁷ cm/s, due to increased population of upper valleys. This result clearly demonstrates the significant role of nonequilibrium Γ-valley transport in determining the high-speed performance of InP/InGaAs DHBT´s