Noise properties of AlGaAs/GaAs HPTs with transparent ITO emitter contacts

The spectra of different excess noise sources are measured and analysed in AlGaAs/GaAs heterophototransistors with the transparent ITO emitter contact in the dark and under illumination. The 1/f (or burst) fluctuations of the tunnel-recombination component of the base current are shown to be the main source of the excess noise observed. The wide scatter of the noise data for different devices as well as the saturation of the noise level in a given device at the high current region appear to be typical for this noise. Its cut-off frequency determined for the floating base mode of operation is found to vary from 250 kHz to 30 MHz for different samples and at different collector currents. High doping levels of the emitter and base regions are considered as the main reason for the noise observed.