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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). [ABSTRACT FROM AUTHOR]

We report the stacked quantum cascade laser and detector structures for a monolithic midinfrared sensing device. In the fabricated quantum cascade device, the layer structures for the detector are grown directly on the quantum cascade laser structure. The laser and detector structures thereby are flexibly designed to operate at the same wavelength, without any compensation needed in the way that the active region is designed in the laser and detector. The fabricated monolithic quantum cascade devices exhibit a low threshold current density at the midinfrared wavelength of 5.7 μm. As a result, light emission and detection on the same chip are demonstrated in continuous wave operation at room temperature. [ABSTRACT FROM AUTHOR]