The wavelength threshold of a semiconductor photodetector is determined by the conventional rule λ = hν/Δ, where Δ is the minimum energy gap of the material, or the interfacial energy gap of the heterostructure. In addition, the dark current and noise levels of the detector is also determined by the Δ. Therefore, there is always a trade-off between increased noise levels and longer spectral threshold due to lowering the Δ. It has been recently demonstrated that the standard limit of can be overcome in extended wavelength infrared detectors. Specifically, a detector a photodetector designed with Δ = 0.40 eV ( = 3.1 µm) showed an extended wavelength threshold up to ~68 µm, ~45 µm, and to ~60 µm, under positive, zero, and negative biases respectively, at 5.3K. p-GaAs/AlGaAs heterostructure-based infrared detectors were utilized in this study. A barrier energy offset (δE) between AlGaAs barriers, is found to be necessary for the spectral extension mechanism, where wavelength extension mechanism was not observed on a reference detector without an offset. The dark current, however, was seen to correspond to Δ = 0.40 eV, which was confirmed by a fitting obtained by using a 3D carrier drift model. Further study with a variation in δE and gradient of the AlxGa1-xAs barrier are in progress, which are expected to shed more light on the underlying mechanism of hot carrier effect.


This work was supported in part by the U.S. Army Research Office under Grant No. W911 NF-15-1-0018, and in part by National Science Foundation (NSF) under Grant No. ECCS-1232184.

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