Optical Response of Strained- and Unstrained-Silicon Cold-Electron Bolometers

We describe the optical characterisation of two silicon cold-electron bolometers each consisting of a small (32 × 14 μm) island of degenerately doped siliconwith superconducting aluminium contacts. Radiation is coupled into the silicon absorber with a twin-slot antenna designed to couple to 160-GHz radiation through a silicon lens. Thefirst device has a highly doped silicon absorber, the secondhas a highly doped strained-silicon absorber. Using a novel method of cross-correlating the outputs from two parallel amplifiers, we measure noise-equivalent powers of 3.0× 10−16 and 6.6×10−17 WHz−1/2 for the control and strained device, respectively,when observing radiation from a 77-K source. In the case of the strained device, the noise-equivalent power is limited by the photon noise.