INFRARED OPTICAL-ABSORPTION OF HG1-XCDXTE

The absorption near the fundamental absorption edge of Hg 1-xCdxTe was measured over the composition range 0.205≤x≤0.220 at temperatures from 80 to 300 K. The dispersion of the index of refraction of Hg1-xCdxTe was obtained from the interference pattern. It was found that the absorption tail obeys a modified Urbach's rule and is expressed by α=α0 exp[σ (E-E0)/(T+T0)] for 20≤α (cm-1) ≤1000. The fitting parameters α0, σ, T0, and E0 vary regularly with x. The expression is used to obtain the absorption coefficient and the temperature coefficient of the gap as a function of x and T. Evidence is presented to show that these parameters may be extrapolated to calculate the absorption beyond the measured composition range.