Infrared Absorption of Indium Antimonide

Indium antimonide samples of a wide range of carrier concentrations were measured from {~}5^∘{}K to 500^∘{}K, over a wavelength region of 3 to 35 microns. Experimental results on the shift of the absorption edge in degenerate n-type samples are presented and discussed. Both n-type and p-type samples show the same absorption at long wavelengths, after becoming intrinsic at elevated temperatures. At lower temperatures, the absorption in n-type samples increases with wavelength, whereas in p-type samples it remains practically constant over a wide wavelength region. The absorption coefficient in different samples, n-type or p-type, does not increase proportionately with the carrier concentration. Possible mechanisms for the absorption are discussed.