Dark current and photoresponse characteristics of extended wavelength infrared photodetectors

The dark current and spectral photoresponse thresholds of a semiconductor photodetector are normally determined by the minimum energy gap (Δ) of the material, or the interfacial energy gap of the heterostructure. In this manuscript, we discuss the performance of an asymmetric p-GaAs/AlₓGa1-ₓAs heterostructure-based infrared photodetector, which shows an extended wavelength threshold beyond the limit set by Δ. The measured dark current was found to agree well with fits obtained from a 3D carrier drift model using the designed value of Δ ∼ 0.40 eV (∼3.1 μm). In contrast, the spectral photoresponse showed extended wavelength thresholds of ∼68 μm, ∼45 μm, and ∼60 μm at positive, zero, and negative biases, respectively, at 5.3 K. For a reference (symmetric) photodetector, the dark current was fitted with the designed value of Δ ∼0.30 eV, and excellent agreement was obtained for both the measured dark current and spectral response. This underlies the advantage of using asymmetric infrared photo-detector designs, in which an extension to the detected wavelengths can be obtained with little compromise to the dark current characteristics.