Infrared quantum-cascade detector has broad spectral response

Infrared quantum-cascade detectors (QCDs) with high detectivities tend to have narrow spectral linewidths, due to the means of detection (optical bound-to-bound transitions). Scientists at the University of Neuchâtel (Neuchâtel, Switzerland) and the Fraunhofer Institute of Applied Solid State Physics (Freiberg, Germany) are circumventing this problem by stacking 26 QCD layers, each with a slightly different wavelength range, into one detector, resulting in a device that has a broad wavelength-detection range of 4.7 to 7.4 µm and a background-limited detectivity of 1.55 × 10¹⁰ Jones (1 Jones is 1 cm•Hz^1/2/W) at 110 K.

The structure contains indium gallium arsenide wells and indium aluminum arsenide barriers, with different layers having different doping densities. A 200 × 200 µm² device was tested at temperatures from 10 K to 300 K (room temperature); detectivity ranged from 2.0 × 10¹¹ Jones at 10 K to 5.6 × 10⁶ Jones at room temperature, while responsivity varied between 13 mA/W at 10 K and 1.25 mA/W at room temperature. Using the detector to measure the spectral transmission of sapphire resulted in finding the expected absorption edge at about 6.2 µm. Contact Daniel Hofstetter at daniel.hofstetter@unine.ch.