Measurement of high current density phenomena and velocity overshoot in InP/GaInAs HBTs

Abstract

Electron transport in the collector of InP/GaInAs heterojunction bipolar transistors (HBTs) was experimentally studied in the high current density regime. The average velocity of electrons in the collector was obtained as a function of the collector current density and base collector voltage, and found to be larger than the saturation velocity. Phenomena caused by the base push out (Kirk) effect were observed. It is demonstrated that below the onset of the Kirk effect the injected electron space charge in the collector improved the high frequency performance of the HBT. A new result presented is that the average electron velocity in the collector exhibited a maximum when plotted versus the base collector voltage.