Hot-carrier photodetector beyond spectral limit

The wavelength limit (λ_c) of detection in a conventional photodetector is limited to a characteristic energy (Δ) through the relationship: λ_c = hc/Δ, where Δ also determines the detector noise (dark current) and hence its performance such as the operating temperature. Here, we report an infrared photodetector with an extended operating range (responding beyond the standard spectral threshold) based on a hot-hole energy transfer mechanism. A detector with Δ = 0.32 eV showing a striking response up to 100 μm has been demonstrated, whereas without the hot-carrier effect the threshold should correspond to ~3.9 μm. A detectivity of 7.8×10⁹ cm Hz^1/2/W at 22 μm has been measured at 80 K.