Quantum cascade detectors based on dual-upper-state active regions with a broadband response

We propose broadband quantum cascade detectors based on a dual-upper-state active region design. The dual-upper-state concept is known to produce broad gain in quantum cascade lasers and is also expected to provide a wide spectral response for quantum cascade detectors. Compared with quantum cascade detectors employing a bound-to-bound design, dual-upper-state devices are anticipated to exhibit broader bandwidth and can achieve higher responsivity. To validate this, we designed and fabricated quantum cascade detectors for each mid-wave (∼5 μm) and long-wave (∼10 μm) infrared regions, implementing anti-crossed dual-upper states in the main absorbing transition. At 300 K, the fabricated devices exhibited responsivities of ∼13.5 mA/W at λpeak ∼5.1 μm and ∼7.1 mA/W at λpeak ∼10 μm. The measured relative bandwidth of the devices Δλ/λcenter are approximately ∼20.8% and ∼21.1%. These results indicate that the dual-upper-state not only enables a wide spectral response but also may provide enhanced responsivity. The experimental findings are further supported by non-equilibrium Green's function simulations. Overall, our results highlight the potential of the dual-upper-state approach for broadband, high-performance infrared detection.