Low-frequency noise of InP/InGaAs heterojunction bipolar transistors

The equivalent base noise SIb of InP/InGaAs heterojunction bipolar transistors (HBT's) with a circular pattern emitter is investigated experimentally at a low frequency ranging front 10-10(5) Hz, The measured SIb, exhibits the 1/f dependence in an overall frequency range without any accompanying burst noise. Furthermore, SIb varies as I-b(gamma) for the base current I-b and as d(-2) for the emitter diameter d, where the value of gamma ranges from 1.62-1.72 depending on d of HBT's used. The 1/f noise model, which rigorously deals with the recombination current at the base surface I-bs as a function of I-b as well as of d is proposed. Applying our noise model to the dependence of SIb on I-b, as well as on d, reveals that even though gamma is less than two, the origin of SIb is due to the recombination of electrons at the exposed base surface near the emitter edges. On the basis of theoretical considerations for the diffusion length of electrons and traps at the base surface, the Hooge parameter alpha(H) for the noise due to the base surface recombination is deduced to be in the order of 10(-2) for the first time.