Tunable hot-carrier photodetectors for terahertz frequency operation

The cut-off wavelength limit (λc) in traditional photodetectors is determined by the activation energy (Δ) of the semiconductor structure, and is given by the relationship: λc = hc/Δ. This empirical spectral rule has dominated device design for many years, and was thought to limit intrinsically the long wavelength response of a photodetector. Recently, however, we have demonstrated a new, long wavelength photodetection principle using a hot-cold carrier energy transfer mechanism. Hot carriers injected into a semiconductor structure interact with cold carriers and excite them to higher energy states. This has enabled a very long-wavelength infrared response up to 55 μm to be achieved, which is tunable by varying the degree of hot-hole carrier injection.