Temperature dependences of current gains in GaInP/GaAs and AlGaAs/GaAs heterojunction bipolar transistors

The temperature dependences of current gain are investigated for both GaInP/GaAs and AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Measured results indicate that for GaInP/GaAs HBTs the current gain at collector current densities >0.1 A/cm/sup 2/ remains nearly constant, independent of the substrate temperature for AlGaAs/GaAs HBTs. These current gain characteristics are examined, and the origin of the difference is attributed to the difference of the valence-band discontinuities in the base-emitter heterojunctions of the two HBTs.>