Source identification and control of 1/f noise in AlGaAs/GaAs HBTs by using an on-ledge Schottky diode

Our experimental results indicate that the 1/f noise spectra density of HBT s is strongly influenced by the emitter ledge potential. By biasing an on-l edge Schottky diode, we fan externally control the ledge potential and alte r HBT's lif noise spectra density and its dependence on the base current. W hen biasing the on-ledge diode at V-L < V-BE, HBT's 1/f noise spectra densi ties are found to increase dramatically (up to 30 dB) from the unbiased val ue and exhibit stronger dependence on Ig (from I-B(1.42) to I-B(1.84)). Whe n biasing the on-ledge diode at V-L > V-BE, HBT's 1/f noise spectra density is found to decrease (about 10 dB) and exhibit virtually no dependence on Ig (from I-B(1.42) to I-B(0.18)). These findings help us identify the sourc es of the 1/f noise and create a novel four-terminal HBT (with an extra led ge electrode) for extremely low 1/f noise RF transceiver applications.