Reflectometry Measurements of the Loss Tangent in Silicon at Millimeter Wavelengths

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We report here on measurements of the reflectivity and loss tangent measured in the W-band (80-125 GHz) and D-band (125-180 GHz) in two samples of float zone silicon with intrinsic stoichiometry - one irradiated by neutrons, which increases the resistivity by introducing crystalline defects, and the other unperturbed.

• We find a loss tangent $\tan(\delta)$ of 2.8e-4 and 1.5e-5 for neutron-irradiated silicon and intrinsic silicon, respectively, both with an index of refraction of 3.41.
• The results demonstrate the applicability of silicon as a warm optical component in millimeter-wave receivers.
• For our measurements, we use a coherent reflectometer to measure the Fabry-Perot interference fringes of the reflected signal from dielectric slabs.