Measurement and comparison of 1/f noise and g-r noise in silicon homojunction and III-V heterojunction bipolar transistors

This paper experimentally determines and compares the 1/f noise and the g-r noise, as components of the base noise current spectral density, in Si homojunction and III-V heterojunction bipolar transistors (HBT's) in common-emitter configuration, The noise spectra for each of these devices are obtained as functions of the base bias current (I-B), and the 1/f noise has been found to depend on I-B as I-B(gamma), where gamma similar to 1.8 for the silicon BJT's and InP/InGaAs HBT's with high current gains (beta similar to 50), and gamma similar to 1.1 for the AlGaAs/GaAs HBT's with low current gains (4 < beta < 12). The nearly constant current gain and the near square-law and inverse-square emitter area dependence of 1/f noise in silicon devices are indicative of the dominant base bulk recombination nature of this noise. The 1/f noise in the InP based HBT's has been found to be lowest among all the devices we have tested, and its origin is suggested to be the base bulk recombination as in the Si devices. For the AlGaAs/GaAs HBT's, the low current gain and the near unity value of gamma arise most likely due to the combined effects of surface, bulk, and depletion region recombinations and the base-to-emitter injection, The dependence of the 1/f noise on the base current density in the devices tested in this work, and those tested by others are compared to find out which HBT's have achieved the lowest level of 1/f noise.