The ability of modulation-doped AlGaAs/GaAs heterojunctions to detect far-IR radiation has been known for almost two decades, but only recently has the technology evolved into a high-sensitivity, narrowband tunable photodetector. Researchers at the University of Tokyo have constructed and evaluated such a device, called a quantum Hall photodetector, and found that it is 1000 times as responsive as a commercially available bolometer at the same temperature.

Using a NiCr film heater deposited on one side of a thin sapphire plate as a controlled far-IR source, the team found that the detector had a responsiveness as high as 1.1 x 10⁷ V/W and a detectivity as high as 4.0 x 10¹³ cm Hz^1/2/W at 4.2 K. The results appear in the Jan. 7 issue of Applied Physics Letters.