Mid-infrared photodetectors operating over an extended wavelength range up to 90 K.

We report a wavelength threshold extension, from the designed value of 3.1 to 8.9 µm, in a p-type heterostructure photodetector. This is associated with the use of a graded barrier and barrier offset, and arises from hole-hole interactions in the detector absorber. Experiments show that using long-pass filters to tune the energies of incident photons gives rise to changes in the intensity of the response. This demonstrates an alternative approach to achieving tuning of the photodetector response without the need to adjust the characteristic energy that is determined by the band structure.