<title>Improvement of low-temperature sensing realized with a superlattice infrared photodetector</title>

It's found that the temperature accuracy (∆ T), measured by the photocurrent ratio of two linearly independent spectral responses, depends on two factors. One is the dissimilarity of the spectral responses determined primarily by the separation of the long and short wavelength peaks, and is not related with their responsivity magnitude. The other is dominated by the smaller S/N between the two measured photocurrents. The dissimilarity can be improved by moving the short wavelength peak to an even shorter one. However, this decreases the signal magnitude measured by the shorter wavelength peak at low target temperature, and results in the degradation of the S/N and ∆ T. Therefore, a superlattice structure with absorption peaks at 6.7µ ma nd 9.7µm is designed, and the wavelength separation is less than the conventional two-color QWIP. The spectral response of the detector is voltage-tunable through a current blocking layer that acts as an energy filter for the photo-excited carriers. The measured peak detectivity of this detector is 3.7 × 10 9 cmHz 0.5 /W (9.7µm) at -0.5V and 2.2× 10 10 cmHz 0.5 /W (6.7µm) at -0.1V at 45K. Our detector is capable of measuring target temperatures ranging from 300K to 1200K and higher. The estimated ∆ T is 0.8K for 300K target, and 0.17K for 1200K target.