Ultimate response time in mid-infrared high-speed low-noise quantum cascade detectors

The ultimate response time in the active region of quantum cascade detectors (QCDs) with a peak response wavelength of 4.5 μm operating at room temperature is determined to be as short as one picosecond, by a comparison of the experimentally determined response time with the theoretical prediction based on an equivalent circuit model. The intrinsic response time of 1 ps is attributed to the electron transit time across only one module in the active region that contains a large number of cascade modules, that is, 45–90 cascade modules in the present QCDs. Therefore, the 3-dB cutoff frequency of the present QCDs is expected to be extremely high, that is, fcutoff ∼160 GHz (1/2πfcutoff ∼1 ps).