Spectral threshold extended photoresponse in asymmetrical p-GaAs/AlGaAs heterostructure-based infrared detectors*

The spectral photoresponse threshold $\lambda_{t} $ of a semiconductor photodetector is conventionally determined by $\lambda_{t} =hc/\Delta $, where $\Delta $ is the minimum energy gap of a material, or the interfacial energy gap of a heterostructure. In addition, the $\Delta $ at the material interface is the key parameter to determine the dark current and noise levels of the detector. Therefore, lowering the $\Delta $ to detect longer spectral region will have a trade-off with increased noise levels. Here, we present infrared detection in very-long-wavelength infrared (VLWIR) in a detector designed with a $\Delta $ for mid-infrared (MIR) region, in p-GaAs/AlGaAs heterostructures. Specifically, a detector designed with $\Delta \quad =$ 0.40 eV ($\lambda_{t} =$ 3.1 \textmu m) showed an extended wavelength threshold up to 68 \textmu m, 45 \textmu m, and 60 \textmu m, under positive, zero, and negative biases respectively, at 5.3K. The dark current, however, was seen to correspond to $\Delta =$ 0.40 eV, which was confirmed by a fitting obtained by using a 3D carrier drift model.