1/f noise characteristics of AlGaAs/GaAs heterojunction bipolar transistor with a noise corner frequency below 1 kHz

The internal low-frequency noise sources of AlGaAs/GaAs HBT's are related to the detailed epi-layer structure as well as surface recombination velocity fluctuation at the extrinsic GaAs base surface. HBT's with a large emitter size of 120 x 120 mu m(2) are fabricated on abrupt emitter-base junction materials without undoped spacer, and the HBT's exhibit an internal noise corner frequency of 100 Hz, which is much lower than about 100 kHz of conventional AlGaAs/GaAs HBT's. The existence of resistance fluctuation 1/f noise is clearly verified by the simple comparison of collector current noise spectra with the varying base termination. It is found that, at a high emitter-base bias, the resistance fluctuation 1/f noise becomes dominant for shorted base-emitter termination, but the internal 1/f noise dominant for open base. To improve the low-frequency noise characteristics for a practical small feature size HBT, device design rules including resistance fluctuation are discussed.