Temperature dependence of current gain in AlGaAs/GaAs heterojunction bipolar transistors

Abstract

Details of the temperature dependence of current gain in AlGaAs/GaAs heterojunction bipolar transistors (HBT’s) are reported for the first time. Unlike homojunction transistors, the gain initially increases with decreasing temperature from 425 K followed by a decrease towards 77 K at a temperature which is dependent on AlAs mole fraction in the emitter. Variation of gain with temperature is much smaller than what is normally seen in homojunction transistors adding another advantage in favor of the HBT’s. Hole injection current into the emitter and parasitic recombination currents are shown to be the reasons for the observed temperature dependence of gain.