Mid-infrared quantum cascade detectors on InP

We report on the characteristics of two InP-based quantum cascade detectors (QCDs) whose responses are centered at 5.35 and 9 mu m. The working principle is based on a vertical intersubband transition followed by a carefully designed extraction cascade, which is adapted to the LO-phonon energy. This device architecture leads to 10 K responsivities R of 8 and 26 mA/W and background limited detectivities D*(BLIP) of 1.7 x 10(10) and 0.9 x 10(10) jones, for the 5.35 mu m and the 9 gm device, respectively. The temperature up to which background limited operation is seen is 115 K for the 5.35 mu m device and roughly 65 K for the 9 mu m detector. Designed for zero bias operation, QCDs produce a minimal dark current and therefore suffer very little from dark current noise. In addition, capacitance saturation at long integration times can be avoided, making them ideal devices for large focal plane arrays. The 5.35 mu m detector was tested at high speed and room temperature. An optical beating signal generated by two slightly de-tuned singlemode quantum cascade lasers was used to test the detector's response at frequencies of up to 23 GHz.