Energy Gap in Hg1−xCdxTe by Optical Absorption

The absorption coefficient at the fundamental absorption edge has been measured in Hg_1−xCd_xTe over the composition range 0.23≤x≤0.61 and at temperatures from 300° to 10°K. The energy gap, estimated from the position of the absorption edge, increases continuously with increasing CdTe content but was not linear between the values for HgTe and CdTe. The energy gap of the alloys varied approximately linearly with temperature for T>100°K, going from a positive temperature coefficient for x0.5. The temperature coefficient of the gap, dE_g/dT, was linear with composition and extrapolated to +5.6×10⁻⁴ eV/°K for HgTe. The expression $$E_g{\text{(x,\hspace{0.17em}T)=−0.303+1.73x+5.6×10}}^{\text{−4}}{\text{(1−2x)T+0.25x}}^4$$ was obtained from the data and can be used to obtain the energy gap as a function of x and T over a large range of these variables.