Submillimeter wave absorption of n-type InSb at low temperatures

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Abstract
The absorption coefficient of two high‐purity n‐InSb samples is measured in the 10–40 cm−1 range using Fourier transform spectroscopy. The absorption coefficient spectrum is presented for both samples at 4.2 K. It is also shown for the lower resistance sample cooled to 2.2 K and heated by dc bias to elevated electron gas temperatures of 7.5 and 17.9 K. ac Drude theory gives rather poor agreement with experiment at 2.2 and 4.2 K but does much better when the sample electron gas is heated. In contrast, a simple quantum mechanical theory of absorption based on inverse Bremsstrahlung yields promising agreement at the lower temperatures although its applicability is questionable. The non‐Drudian absorption is shown to have a favorable effect on the performance of InSb hot‐electron bolometers.