Noise characterization of AlGaAs/GaAs HBTs with different emitter contacts

The results of comparative investigations of the noise spectra of AlGaAs/GaAs HBTs with the optically transparent indium tin oxide (ITO) emitter contact and with the ordinary (opaque) emitter contact are presented. The measurements were carried out in the dark and under illumination in different transistor configurations and at different currents. This made it possible to detect the 1/f noise that is generated at the ITO contact and that is absent at the ordinary contact. It has been revealed that not only the emitter contact noise but also the noise generated in the emitter and even in the collector junctions of the HBTs with ITO contacts are much higher than in the devices with the ordinary contacts. It is also found that the excess noise of the base current in the devices of both types is much lower than in the AlGaAs/GaAs HBTs described in the literature and, hence, the HBTs investigated have improved noise performance for broad band circuit application.