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/sub L/V/sub BE/, the HBT 1/f noise spectral density is found to decrease (about 10 dB) and exhibit virtually no dependence on I/sub B/ (from I/sub B//sup 1.42/ to I/sub B//sup 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.