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/spl times/10/sup -14/ W/Hz/sup 1/2/ from this phototransistor with bias of 4.0 V at a wavelength of 2.05 /spl mu/m were measured at 20/spl deg/C and -20/spl deg/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 /spl mu/W/cm/sup 2/ and of 30 mA at high intensity of 100 mW/cm/sup 2/ 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-/spl mu/W input power range is achieved, which demonstrates high dynamic range for such devices at these power levels.