Low-frequency noise of InP/InGaAs heterojunction bipolar transistors

The equivalent base noise SI/sub b/ of InP/InGaAs heterojunction bipolar transistors (HBT's) with a circular pattern emitter is investigated experimentally at a low frequency ranging from 10-10/sup 5/ Hz. The measured SI/sub b/ exhibits the 1/f dependence in an overall frequency range without any accompanying burst noise. Furthermore, SI/sub b/ varies as I/sub b//sup /spl gamma// for the base current I/sub b/ and as d/sup -2/ for the emitter diameter d, where the value of /spl 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/sub bs/ as a function of I/sub b/ as well as of d is proposed. Applying our noise model to the dependence of SI/sub b/ on I/sub b/, as well as on d, reveals that even though /spl gamma/ is less than two, the origin of SI/sub b/ 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 /spl alpha//sub H/ for the noise due to the base surface recombination is deduced to be in the order of 10/sup -2/ for the first time.