Emitter-Base Junction Size Effect on Current Gain Hfe of AlGaAs/GaAs Heterojunction Bipolar Transistors

A current gain reduction with emitter-base junction size decrease is found in uniform base AlGaAs/GaAs heterojunction bipolar transistors (HBTs). This characteristic is analyzed using a model that takes into account a lateral diffusion of injected electrons, and is shown to be well explained by this model. The results show the importance of excess base leakage current due to minority carrier recombinations in the external bases of uniform base HBTs.