In the middle and late 1950s it was discovered that InSb had the smallest energy gap of any semiconductor known at that time and its applications as a middle wavelength infrared detector became obvious [1,2]. The energy gap of InSb is less well matched to the 3-5 µm band at higher operating temperatures, and better performance can be obtained from Hg1-xCdxTe. InAs is a similar compound to InSb, but has a larger energy gap [3], so that the threshold wavelength is 3-4 µm, and both photoconductive and photovoltaic detectors have been fabricated. The photoconductive process in InSb has been studied extensively, and more details can be found in Morten and King [4], Kruse [5], and Elliott and Gordon [6].