InGaAsSb/AlGaAsSb heterojunction phototransistors for infrared applications

High quality infrared (IR) quantum detectors are important for several applications, such as atmospheric remote sensing, chemical detection and absorption spectroscopy. Although several IR detectors are commercially available, with different materials and structures, they provide limited performance regarding the signal-to-noise ratio and the corresponding minimum detectable signal. InGaAsSb/AlGaAsSb heterojunction based phototransistors show strong potential for developing IR sensors with improved performance. In this paper, the performance of a novel n-p-n InGaAsSb/AlGaAsSb heterojunction phototransistor is presented. This performance study is based on experimental characterization of the device dark current, noise and spectral response. Detectivity of 1.7x109 cmHz 1/2/W at 2-μm was obtained at 100°C temperature and 2 V bias voltage. This corresponds to a responsivity of 94.7 A/W and an internal gain of 156 with about 38% quantum efficiency. Reducing the temperature to -30°C allows to increase the bias to 3V and enhance the detectivity to 8.7x1010 cmHz1/2/W at the same wavelength, which corresponds to a responsivity of 386.5 A/W and an internal gain of 288.2 with about 83% quantum efficiency. The device impulse response and linearity, including the corresponding dynamic range, also are presented. Impulse response analysis indicated a settling time of about 1.1 μs at 2V and 100°C, while linearity measurements indicated a constant responsivity in the radiation intensity range of 1.6x10-7 W/cm2 and 31.6 mW/cm2.