The effect of n-GaAs carrier concentration on current gain in InGaP/GaAs heterojunction bipolar transistors

The effect of n-GaAs carrier concentration in the Si-doped sub-collector layer on InGaP/GaAs heterojunction bipolar transistor (HBT) was investigated. Current gain slightly decreased with carrier concentration increased from 5 x 10(17) to 2 x 10(18) cm(-3), while it dramatically decreased with carrier concentration increased over 2 x 10(18) cm(-3). It was also found that current gain with a high carrier concentration of 4 x 10(18) cm(-3) decreased with annealing time. Gummel plots revealed that the reduction in current gain is caused by creation of recombination centers in the base layer. We suggest the diffusion of Ga interstitial, which is generated together with Ga vacancy, is the origin of current gain degradation during the post-growth of the sub-collector layer.