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 (HBT's). Measured results indicate that for GaInP/GaAs HBT's the current gain at collector current densities > 0.1 A/cm2 remains nearly constant, in dependent of the substrate temperature. In contrast, the current gain decreases monotonically with temperature for AlGaAs/GaAs HBT's. These current gain characteristics are examined and the origin of the differ ence is attributed to the difference of the valence-band discontinuiti es in the base-emitter heterojunctions of the two HBT's.