Abstract
We describe the optical characterisation of two silicon cold-electron bolometers each consisting of a small ($32 \times 14~\mathrm{\mu m}$) island of degenerately doped silicon with 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.The first device has a highly doped silicon absorber, the second has 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 $3.0 \times 10^{-16}$ and $6.6 \times 10^{-17}~\mathrm{W\,Hz^{-1/2}}$ 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.
Highlights
The cold-electron bolometer is a broadband bolometric detector where the only fundamental limit to the frequency response comes from the spectral transmission of the absorber
In order to measure the noise of the devices themselves, we present a novel concept of cross-correlating the outputs of two matched JFET amplifiers to remove the uncorrelated amplifier noise leaving only the device noise
To compare the strained- and unstrained-silicon cold-electron bolometers, both current–voltage (I –V ) characteristics as well as noise spectra of the devices have been measured, these measurements have been performed in dark and in the presence of optical power
Summary
The cold-electron bolometer is a broadband bolometric detector where the only fundamental limit to the frequency response comes from the spectral transmission of the absorber. The original, and still most common, cold-electron bolometer design involved a normalmetal absorber with tunnelling contacts to superconducting leads; see, for example, the work of Kuzmin [1] This structure has been used in the so-called microrefrigerator devices to cool electrons below the lattice temperature. It has been shown that introducing strain into the silicon lattice can further reduce this coupling, allowing microrefrigerator-type devices to achieve lower electron temperatures compared to unstrained-silicon [4] Based on this lower electron temperature achieved using strained-silicon, it is expected that the responsivity of cold-electron bolometer based on strained-silicon should be higher than a comparable detector utilising unstrained-silicon. We take two devices: the control device using doped silicon, and a device where the doped absorber is strained by a layer of Si0.8Ge0.2 We compare these devices by characterising them in a dark environment and when illuminated. In order to measure the noise of the devices themselves, we present a novel concept of cross-correlating the outputs of two matched JFET amplifiers to remove the uncorrelated amplifier noise leaving only the device noise
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