Temperature dependence of the fundamental absorption edge of mercury cadmium telluride

We have investigated the temperature dependence of the fundamental absorption edge of a series of Hg1−xCdxTe alloys (with composition x ranging from 0.5 to 1). Analyzing our data in the light of the three‐dimensional theory of direct‐allowed excitons, we find precise values for the fundamental Γ8‐Γ6 interband transition energy in a temperature range extending from 0 to 300 K. All experimental results, including previous data for HgTe and mercury‐rich Hg1−xCdxTe alloys, are well accounted for using a simple empirical formula: Eg (eV)=−0.303(1−x)+1.606x−0.132x(1−x)+[6.3(1−x) −3.25x −5.92x(1−x)]10−4T2/[11(1−x)+78.7x+T]. This expression, which is valid for all compositions 0≤x≤1 and temperatures 0≤T≤500 K, predicts an alloy composition such that the band‐gap energy is temperature independent: We find x=0.505. Finally, it can be used for technological application purpose (far‐infrared detection as well as optical‐fiber communications performed at realistic values of the temperature) and gives accurate values f...