Abstract
The influence of an undoped spacer layer in the emitter-base junction on HBT characteristics was investigated experimentally and theoretically. The ideality factor n of the base current increased from 1.1 to 1.9 for an undoped spacer-layer thickness of between 25 and 150Å. This indicates that the increment of the depletion-layer thickness in GaAs base-side produces a g-r current enhancement in the EB junction. The theoretical analysis also suggests these tendencies. The calculation shows that the n value variation is caused by a one-sided distribution of carriers due to an energy barrier at the heterojunction.