Thanks to recent advances in normal-incidence infrared quantum dot detectors (QDIPs), these devices are emerging as a promising technology for midwave- and longwave-infrared sensing and spectral imaging. Based on intersubband transitions in nanoscale self-assembled systems, QDIPs have shown a broad spectral response that is bias dependent. While the broad spectral coverage is advantageous for broadband forward looking infrared (FLIR) imaging, it is disadvantageous for applications that require narrow spectral resolution such as chemical agent detection. On the other hand, the bias-dependent feature of the spectral response, as seen in certain QDIP devices with a dot-in-a-well (DWELL) structure [1], can be exploited by post-processing algorithms to achieve a high level of spectral tuning and matched filtering. As seen Fig. 1, the detector's responsivity changes continuously in its center wavelength and shape with the applied bias. The bias-dependent nature of the QDIP responsivity is due to the quantum-confined Stark effect, which is caused by an asymmetric potential profile in the DWELL structure. For this type of QDIPs, a single detector can be operated at multiple biases sequentially, whereby the detector's responsivity changes each time the bias is varied. Therefore, a single QDIP detector can be exploited as different detectors; and, photocurrents of a single QDIP, driven by different operational biases, can be viewed as outputs of different spectrally overlapping bands.
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