1/f noise of AlGaAs-GaAs HBTs controlled by biasing an on-ledge Schottky diode

Experimental results indicate that the 1/f noise spectral density of HBTs is strongly influenced by the emitter ledge potential. By biasing an on-ledge Schottky diode, we can externally control the ledge potential and alter an HBT´s 1/f noise spectral density and its dependence on the base current. When biasing the on-ledge diode at V_L<V_BE, HBT 1/f noise spectral densities are found to increase dramatically (up to 30 dB) from the unbiased value and exhibit stronger dependence on I_B (from I_B^1.42 to I_B^1.84). When biasing the on-ledge diode at V_L>V_BE, the HBT 1/f noise spectral density is found to decrease (about 10 dB) and exhibit virtually no dependence on I_B (from I_B^1.42 to I_B^0.18). These findings help us identify the sources of the 1/f noise and create a novel 4-terminal HBT (with an extra ledge electrode) for extremely low 1/f noise RF transceiver applications