AlGaAsSb-InGaAsSb HPTs with high optical gain and wide dynamic range

Novel heterojunction phototransistors based on AlGaAsSb-InGaAsSb material systems are fabricated and their characteristics are demonstrated. Responsivity of a phototransistor is measured with applied bias voltage at four different wavelengths. The maximum responsivity around 1400 A/W and minimum noise equivalent power of 1.83×10^-14 W/Hz¹2/ from this phototransistor with bias of 4.0 V at a wavelength of 2.05 μm were measured at 20°C and -20°C, respectively. Noise equivalent power of the phototransistor is considerably lower compared with commercially available InGaAs p-i-n photodiodes. Collector current measurements with applied incident power are performed for two phototransistors. Currents of 400 nA at low intensity of 0.425 μW/cm² and of 30 mA at high intensity of 100 mW/cm² are determined. Collector current increases nearly by five orders of magnitude between these two input intensities. High and constant optical gain of 500 in the 0.46-nW to 40-μW input power range is achieved, which demonstrates high dynamic range for such devices at these power levels.